plugins/elements/: Special case the "file://" URI as as this is used by some applicat...

plugins/elements/: Special case the "file://" URI as as this is used by some applications to test with gst_element_ma...

Original commit message from CVS:
* plugins/elements/gstfilesink.c: (gst_file_sink_uri_set_uri):
* plugins/elements/gstfilesrc.c: (gst_file_src_uri_set_uri):
Special case the "file://" URI as as this is used by some
applications to test with gst_element_make_from_uri if there's
an element that supports the URI protocol.
Also move the g_path_is_absolute() check for the location part
of the URI to also check this for "file://localhost/bla" URIs.