various win32 odds and ends

various win32 odds and ends
 - added support for waitpid(), open2/open3, and a bugfix for kill()
   from Ronald Schmidt <RonaldWS@aol.com>
 - tweak testsuite mods of above
 - regenerate win32/config_H.?c
 - change kill() to win32_kill() and export it
 - coalesce common code in win32.c
 - add PerlProc_waitpid() and export win32_waitpid()
result builds and passes on the three win32 compilers

p4raw-id: //depot/perl@1134