API: add new libgstbaseutils library with functions

API: add new libgstbaseutils library with functions

Original commit message from CVS:
* configure.ac:
* gst-libs/gst/Makefile.am:
* gst-libs/gst/utils/Makefile.am:
* gst-libs/gst/utils/base-utils.c: (gst_base_utils_init):
* gst-libs/gst/utils/base-utils.h:
* gst-libs/gst/utils/descriptions.c: (format_info_get_desc),
(find_format_info), (caps_are_rtp_caps),
(gst_base_utils_get_source_description),
(gst_base_utils_get_sink_description),
(gst_base_utils_get_decoder_description),
(gst_base_utils_get_encoder_description),
(gst_base_utils_get_element_description),
(gst_base_utils_add_codec_description_to_tag_list),
(gst_base_utils_get_codec_description), (gst_base_utils_list_all):
* gst-libs/gst/utils/descriptions.h:
* gst-libs/gst/utils/missing-plugins.c:
(missing_structure_get_type), (copy_and_clean_caps),
(gst_missing_uri_source_message_new),
(gst_missing_uri_sink_message_new),
(gst_missing_element_message_new),
(gst_missing_decoder_message_new),
(gst_missing_encoder_message_new),
(missing_structure_get_string_detail),
(missing_structure_get_caps_detail),
(gst_missing_plugin_message_get_installer_detail),
(gst_missing_plugin_message_get_description),
(gst_is_missing_plugin_message):
* gst-libs/gst/utils/missing-plugins.h:
API: add new libgstbaseutils library with functions
- to create and parse missing-plugins messages
- that provide (translated) descriptions for caps/decoders/sources/etc.
Closes #392393.
* pkgconfig/gstreamer-plugins-base-uninstalled.pc.in:
* pkgconfig/gstreamer-plugins-base.pc.in:
Add new lib.
* docs/libs/gst-plugins-base-libs-docs.sgml:
* docs/libs/gst-plugins-base-libs-sections.txt:
Generate docs for new lib and API.
* tests/check/Makefile.am:
* tests/check/libs/.cvsignore:
* tests/check/libs/utils.c: (missing_msg_check_getters),
(GST_START_TEST), (libgstbaseutils_suite):
Add some basic unit tests.