API: add GstParamSpecFraction, so elements can have fraction properties without lots of painful string parsing (#4446...

Original commit message from CVS:
* docs/gst/gstreamer-sections.txt:
* gst/Makefile.am:
* gst/gst.c:
* gst/gst.h:
* gst/gstparamspecs.c: (_gst_param_fraction_init),
(_gst_param_fraction_set_default), (_gst_param_fraction_validate),
(_gst_param_fraction_values_cmp),
(gst_param_spec_fraction_get_type), (gst_param_spec_fraction):
* gst/gstparamspecs.h:
* gst/gstvalue.c:
* tests/check/Makefile.am:
* tests/check/gst/.cvsignore:
* tests/check/gst/gstparamspecs.c: (gst_dummy_obj_base_init),
(gst_dummy_obj_class_init), (gst_dummy_obj_init),
(gst_dummy_obj_set_property), (gst_dummy_obj_get_property),
(GST_START_TEST), (gst_param_spec_suite):
API: add GstParamSpecFraction, so elements can have fraction
properties without lots of painful string parsing (#444648).