wined3d: Add a function to determine if a surface is the front or the backbuffer for a swapchain, and return the corresponding GLenum.

This implements a basic more, eg 'dir | more' or 'more file.c'
but it does not support the flags or keys which can control it.
Basically its not worth implementing those, as in some modes
we cannot read a single key, we have to wait for <enter> anyway.

- Added tests for empty and zero-byte strings. Wine passes these tests, sort of.
- Check that the returned string is correct.
- All known Windows versions implement RegQueryValueExA(), so complain if it is not implemented.
- Only allow the Win9x quirks for the Ansi version.
- Query the name2A/W value for the string2A/W tests!
- The test_hkey_main_Value_A/W() functions were doing a sizeof() on the string parameter to compute the string's full size!
- We must reset GLE before each test, otherwise Win9x skips all but the first test.