Make giomm tests Run Under Windows

/etc/fstab is a *nix only file, which would not normally exist under
Windows unless one is under Cygwin.  Use the path for the Wordpad
application on Windows, which is a standard part of Windows; and use
/etc/fstab otherwise.

	* tests/giomm_ioerror/main.cc:
	* tests/giomm_simple/main.cc: Test for c:/windows/write.exe
	  (Wordpad application) on Windows, and use /etc/fstab otherwise.

https://bugzilla.gnome.org/show_bug.cgi?id=736778

https://bugzilla.gnome.org/show_bug.cgi?id=736778