[SETUPLIB] Additions for filesup.c and inicache.c.

[SETUPLIB] Additions for filesup.c and inicache.c.

- In DoesFileExist(): Call NtOpenFile with FILE_GENERIC_READ instead of the more generic GENERIC_READ access right.
- OpenAndMapFile(): Add support for opening & mapping files with write access (to be used latter).

svn path=/branches/setup_improvements/; revision=74710

- Split IniCacheLoad() and IniCacheSave() into: themselves & IniCacheLoadByHandle() and IniCacheSaveByHandle(),
  respectively, so that we can load & save INI files if we already have an opened handle to them.

svn path=/branches/setup_improvements/; revision=74711