gst/gstregistry.c: Plugin extension on HP-UX is .sl, add that to the list of approved...

gst/gstregistry.c: Plugin extension on HP-UX is .sl, add that to the list of approved plugin extensions (see #393796).

Original commit message from CVS:
* gst/gstregistry.c: (gst_registry_scan_path_level):
Plugin extension on HP-UX is .sl, add that to the list of approved
plugin extensions (see #393796).
* tests/check/gst/gstpad.c: (GST_START_TEST):
ulong => gulong. Fixes compilation with HP-UX compiler.
* tests/check/pipelines/parse-launch.c: (GST_START_TEST):
Fix compilation if valgrind headers are not available.