Revert "Fix the build"

This reverts commit 5d4342dd14bb7ca79b63c1341fdfa420164b35e4.
Revert "Pass 0 (NULL) instead of  for C properties."

This reverts commit db1668a39d9646882d5aa6b7386a3b7ea70f99af.
Revert "gmmproc: Pass 0 (NULL) instead of  to C functions."

This reverts commit 5acce15576a91aec89c04b8fe5f8532b192acb71.
gmmproc: Pass NULL to C function calls for optional empty strings.

	* tools/pm/Output.pm (convert_args_cpp_to_c): When generating
	conversions for the C++ arguments, if the argument is optional
	and it is a std::string or a Glib::ustring, prepend a check for
	the empty string to the standard conversion, passing NULL to the
	C function if the string is empty.

	Bug #686909.
2.37.7
Port tools/defs_gen to Python 3.

* .gitignore: Ignore /tools/defs_gen/__pycache__/.
* tools/defs_gen/*.py: Port to Python 3. These Python sources now run with
both Python 2 and Python 3. Tested with 2.7.3 and 3.2.3.
Bug #690969.
Merge branch 'master' of git://git.gnome.org/glibmm
JOHNE - Bump version number to 2.37.7