Enable 2 functions in RISC_OSLib shared entry table.
Robert Sprowson authored
Needed by !Paint 2.02.
Fix some easy warnings in wimp.c/sprite.c.
Add new function (not in the ROM version) 'wimp_baseofromsprites()'.
bbc_adval fixed to return -1 when no ADC fitted to match Electron behaviour.
Note: the 2 reenabled functions haven't been appended to the table, so anyone who linked a RAM application against 'romastubs' would need to relink.

Version 5.58. Tagged as 'RISC_OSLib-5_58'
7d3fe675