Fix FindOKMode not recovering properly from unsupported VIDC lists

Detail:
  s/vdu/vduswis - Fix 18 year old register corruption bug in FindOKMode which would prevent it from falling back to Service_ModeTranslation if Service_ModeExtension returned a VIDC list but the VIDC list was rejected by the GraphicsV driver
  s/vdu/vdudriver - Also, change a couple of error cases in ModeChangeSub so that they use the "Screen mode not available" error instead of the incorrect "Not enough screen memory" error.
Admin:
  Tested on Raspberry Pi 3
  Fixes issue reported on forums where if AnyMode is loaded, numbered modes in unsupported colour depths weren't being replaced with substitutes (although note that there are still some AnyMode-related issues to resolve)
  https://www.riscosopen.org/forum/forums/4/topics/12773


Version 6.16. Tagged as 'Kernel-6_16'

VersionASM

@@ -11,13 +11,13 @@
                         GBLS    Module_HelpVersion
                         GBLS    Module_ComponentName
                         GBLS    Module_ComponentPath
-Module_MajorVersion     SETS    "6.15"
-Module_Version          SETA    615
+Module_MajorVersion     SETS    "6.16"
+Module_Version          SETA    616
 Module_MinorVersion     SETS    ""
-Module_Date             SETS    "14 Nov 2018"
-Module_ApplicationDate  SETS    "14-Nov-18"
+Module_Date             SETS    "19 Nov 2018"
+Module_ApplicationDate  SETS    "19-Nov-18"
 Module_ComponentName    SETS    "Kernel"
 Module_ComponentPath    SETS    "apache/RiscOS/Sources/Kernel"
-Module_FullVersion      SETS    "6.15"
-Module_HelpVersion      SETS    "6.15 (14 Nov 2018)"
+Module_FullVersion      SETS    "6.16"
+Module_HelpVersion      SETS    "6.16 (19 Nov 2018)"
                         END

VersionNum

-/* (6.15)
+/* (6.16)
  *
  * This file is automatically maintained by srccommit, do not edit manually.
  * Last processed by srccommit version: 1.1.
  *
  */
-#define Module_MajorVersion_CMHG        6.15
+#define Module_MajorVersion_CMHG        6.16
 #define Module_MinorVersion_CMHG        
-#define Module_Date_CMHG                14 Nov 2018
+#define Module_Date_CMHG                19 Nov 2018
 
-#define Module_MajorVersion             "6.15"
-#define Module_Version                  615
+#define Module_MajorVersion             "6.16"
+#define Module_Version                  616
 #define Module_MinorVersion             ""
-#define Module_Date                     "14 Nov 2018"
+#define Module_Date                     "19 Nov 2018"
 
-#define Module_ApplicationDate          "14-Nov-18"
+#define Module_ApplicationDate          "19-Nov-18"
 
 #define Module_ComponentName            "Kernel"
 #define Module_ComponentPath            "apache/RiscOS/Sources/Kernel"
 
-#define Module_FullVersion              "6.15"
-#define Module_HelpVersion              "6.15 (14 Nov 2018)"
-#define Module_LibraryVersionInfo       "6:15"
+#define Module_FullVersion              "6.16"
+#define Module_HelpVersion              "6.16 (19 Nov 2018)"
+#define Module_LibraryVersionInfo       "6:16"

s/vdu/vdudriver

@@ -683,9 +683,9 @@ ModeChangeSub ROUT
         BL      DoFullVetMode
         Pull    "R2"
         SUB     R13, R13, #12
-        BEQ     %FT06                   ; not supported, complain
+        BEQ     %FT041                  ; not supported, complain
         TST     R0, #GVVetMode2_ExtraBytes_Invalid
-        BNE     %FT06                   ; Service_ModeExtension should have made sure ExtraBytes was valid
+        BNE     %FT041                  ; Service_ModeExtension should have made sure ExtraBytes was valid
         ; R0, R3, R5 may contain important info
         STMIA   R13, {R0, R3, R5}
         AND     R0, R0, #GVVetMode2_ResultMask
@@ -711,8 +711,9 @@ ModeChangeSub ROUT
         SWI     XOS_ChangeDynamicArea
         BVC     %FT08
 06
-        ADD     R13, R13, #PushedInfoSize + 4*4 ; junk stacked info + mode no + vetmode2 info
         ADR     R0, ErrorBlock_BadMODE
+065
+        ADD     R13, R13, #PushedInfoSize + 4*4 ; junk stacked info + mode no + vetmode2 info
       [ International
         BL      TranslateError
       ]
@@ -720,6 +721,10 @@ ModeChangeSub ROUT
         SETV                            ; indicate error
         Pull    PC
 
+041
+        ADRL    R0, ErrorBlock_ModeNotAvailable
+        B       %BT065
+
 045
         CMP     R11, R5
         BHI     %BT06                   ; ext. framestore not big enough

s/vdu/vduswis

@@ -836,6 +836,7 @@ FindOKMode ROUT
         CMP     r0, #&100               ; if it's a mode number
         BICCC   r2, r0, #&80            ; then knock off shadow bit
         MOVCS   r2, r0                  ; else don't
+        MOV     r10, r3
         BL      OfferModeExtension
         BNE     %FT05
 
@@ -858,6 +859,7 @@ FindOKMode ROUT
 04
         CMP   r0,#0
         Pull "r0-r4,r12"
+        MOVNE r3, r10
         BNE   %FT05         ; driver says "Oi, Kernel, No!"
 
 ; service claimed and happy driver so return with this mode