* pex-win32.c: Include "windows.h".
(backslashify): New function.
(fix_argv): Use backslashify to convert path to windows format.  Allocate one
more place in new argv for potential executable from '#!' parsing.
(tack_on_executable): New function.  Conditional on USE_MINGW_MSYS
(openkey): Ditto.
(mingw_rootify): Ditto.
(msys_rootify): Ditto.
(spawn_script): New function.
(pex_win32_exec_child): Save translated argv in newargv.  Pass to spawn_script
if spawnv* fails.
(main): New function.  Conditional on MAIN.  Useful for testing.

From-SVN: r104292