Numerous tweaks and fixes

Detail:
  c/ScrModes:
  - Double-checked all the DMT timings against the spec and corrected a few mistakes in both the DMT timings list and the established timings list.
  - Tidied up DMT & established timing formatting a bit, made static data arrays const
  - Fixed preferred mode handling so that it'll forget the preferred mode if you load an MDF after reading EDID (preferred_mode->bit0 used as a cheeky flag, in preference over malloc/free). Fixes crash/bad behaviour on startup caused by returning a duff preferred mode from Service_MonitorLeadTranslation on startup.
  - Added sanity checks to avoid null pointer dereferences if preferred_mode or new_preferred_mode are null
  - Fixed preferred mode handling to work correctly with interlaced modes (fixed it to use the frame width & height instead of the field width & height)
  - Tweaked CVT extension block handling - swapped the "- 17" with "- 18" in order to take into account the presence of the checksum byte
  - Tweaked GTF calculation to round pixel_khz to nearest when calculating it. I don't think this is mentioned in the spec, but when comparing some timings against the GTF spreadsheet this fixes ScreenModes being off by 1kHz in a few cases
  - When outputing an MDF, don't output display range parameters if the block wasn't found
  - Fix MDF output of interlaced modes (frame width/height vs. field width/height), use more accurate mHz frame rate value instead of Hz one
  - Make GraphicsV_IICOp calls use the correct GraphicsV driver number; current_graphicsv_driver() function added to replace ad-hoc code in a couple of other places
  - Fix reading of extension blocks. Also tweak logic to avoid re-reading the first block.
  - Initialise 'thefilename' when calling parseedid so that ERR_NOMODES will display something vaguely sensible
Admin:
  Tested on Raspberry Pi (ROM), Pandaboard (ROM), Iyonix (softload)
  Appears to read EDID correctly from test monitors (BenQ FP737s, BenQ FP241W, ADI TD-523N), but there are some minor discrepancies in MDF output for some modes


Version 0.43. Tagged as 'ScrModes-0_43'

VersionNum

-/* (0.42)
+/* (0.43)
  *
  * This file is automatically maintained by srccommit, do not edit manually.
  * Last processed by srccommit version: 1.1.
  *
  */
-#define Module_MajorVersion_CMHG        0.42
+#define Module_MajorVersion_CMHG        0.43
 #define Module_MinorVersion_CMHG        
-#define Module_Date_CMHG                12 Feb 2015
+#define Module_Date_CMHG                14 Feb 2015
 
-#define Module_MajorVersion             "0.42"
-#define Module_Version                  42
+#define Module_MajorVersion             "0.43"
+#define Module_Version                  43
 #define Module_MinorVersion             ""
-#define Module_Date                     "12 Feb 2015"
+#define Module_Date                     "14 Feb 2015"
 
-#define Module_ApplicationDate          "12-Feb-15"
+#define Module_ApplicationDate          "14-Feb-15"
 
 #define Module_ComponentName            "ScrModes"
 #define Module_ComponentPath            "castle/RiscOS/Sources/Video/UserI/ScrModes"
 
-#define Module_FullVersion              "0.42"
-#define Module_HelpVersion              "0.42 (12 Feb 2015)"
-#define Module_LibraryVersionInfo       "0:42"
+#define Module_FullVersion              "0.43"
+#define Module_HelpVersion              "0.43 (14 Feb 2015)"
+#define Module_LibraryVersionInfo       "0:43"