* libgimp/gimp.c: No need for <io.h> on Win32.
* libgimp/{gimp,gimpui}.def: Add two entry points.
* libgimp/gimp.h: Can't use __declspec(dllexport) for PLUG_IN_INFO
when compiling with gcc on Win32. Also handle __argc, __argv and
_stdcall differently with gcc on Win32
* libgimp/gimpenv.c: Include <string.h>.
* libgimp/gimpfeatures.h.in: Remove lots of extraneous trailing blanks.
* libgimp/gimpfileselection.c: Include <glib.h> early, see above.
* libgimp/{gimpwire,parasite}.c: Test for NATIVE_WIN32, not
_MSC_VER.
* libgimp/makefile.msc: Miscellaneous updates. The gimpi library
is now built as a static library.