ext/jpeg/gstjpegenc.c: Don't leak input buffer in chain function (fixes #322667); make state change function thread-s...

Original commit message from CVS:
* ext/jpeg/gstjpegenc.c: (gst_jpegenc_resync), (gst_jpegenc_chain),
(gst_jpegenc_set_property), (gst_jpegenc_get_property),
(gst_jpegenc_change_state):
Don't leak input buffer in chain function (fixes #322667); make
state change function thread-safe; don't repeat the current function
name in GST_DEBUG statements; use GST_ROUND_UP_* macros; use
gst_pad_alloc_buffer(); misc. minor cleanups.