Add ability to add attributes to gdb.Objfile and gdb.Progspace objects.

Add ability to add attributes to gdb.Objfile and gdb.Progspace objects.

gdb/ChangeLog:

	* NEWS: Mention ability add attributes to gdb.Objfile and
	gdb.Progspace objects.
	* python/py-objfile.c (objfile_object): New member dict.
	(objfpy_dealloc): Py_XDECREF dict.
	(objfpy_initialize): Initialize dict.
	(objfile_getset): Add __dict__.
	(objfile_object_type): Set tp_dictoffset member.
	* python/py-progspace.c (progspace_object): New member dict.
	(pspy_dealloc): Py_XDECREF dict.
	(pspy_initialize): Initialize dict.
	(pspace_getset): Add __dict__.
	(pspace_object_type): Set tp_dictoffset member.

gdb/doc/ChangeLog:

	* python.texi (Progspaces In Python): Document ability to add
	random attributes to gdb.Progspace objects.
	(Objfiles In Python): Document ability to add random attributes to
	gdb.objfile objects.

gdb/testsuite/ChangeLog:

	* gdb.python/py-objfile.exp: Add tests for setting random attributes
	in objfiles.
	* gdb.python/py-progspace.exp: Add tests for setting random attributes
	in progspaces.