Call overloaded operators to perform operations on gdb.Value objects.

Call overloaded operators to perform operations on gdb.Value objects.

	* NEWS: Add entry for the new feature
	* python/py-value.c (valpy_binop): Call value_x_binop for struct
	and class values.

	testsuite/
	* gdb.python/py-value-cc.cc: Improve test case to enable testing
	operations on gdb.Value objects.
	* gdb.python/py-value-cc.exp: Add new test to test operations on
	gdb.Value objects.

	doc/
	* python.texi (Values From Inferior): Add description about the
	new feature.