Add support for basic and digest authentication in souphttpsrc.

Add support for basic and digest authentication in souphttpsrc.

Original commit message from CVS:
Patch by: Ron McOuat <rmcouat at smartt dot com>
* ext/soup/gstsouphttpsrc.c: (gst_soup_http_src_class_init),
(gst_soup_http_src_init), (gst_soup_http_src_dispose),
(gst_soup_http_src_set_property), (gst_soup_http_src_get_property),
(gst_soup_http_src_authenticate_cb), (gst_soup_http_src_start):
* ext/soup/gstsouphttpsrc.h:
* tests/check/elements/souphttpsrc.c: (basic_auth_cb),
(digest_auth_cb), (run_test), (GST_START_TEST),
(souphttpsrc_suite), (run_server):
Add support for basic and digest authentication in souphttpsrc.
Fixes bug #561775.