libs/gst/check/gstcheck.c: if we get the wrong message, give us the types as string

libs/gst/check/gstcheck.c: if we get the wrong message, give us the types as string

Original commit message from CVS:
* libs/gst/check/gstcheck.c: (gst_check_message_error),
(gst_check_run_suite):
if we get the wrong message, give us the types as string
* plugins/elements/gstfilesrc.c: (gst_file_src_start):
Fix a translatable
* tests/check/elements/filesrc.c: (GST_START_TEST):
add a test for trying to open a non-existing file