core, w32: Enable spawning GUI applications
* src/engine-spawn.c (engspawn_start): Translate spawn flag to IOSPAWN flag. * src/gpgme-w32spawn.c (my_spawn): Handle the new flag. * src/gpgme.h.in (GPGME_SPAWN_SHOW_WINDOW): New. * src/priv-io.h (IOSPAWN_FLAG_SHOW_WINDOW): New.
Used by GpgOL