mpegts: only reopen pmt_cb filter if its different from the previous.

Fixes Ticket2632

Signed-off-by: Michael Niedermayer <michaelni@gmx.at>
(cherry picked from commit b009267910df10c004b5f340a090d45da29089a0)
mpeg12dec: avoid reinitialization on PS changes when possible.

Fixes Ticket2574

Signed-off-by: Michael Niedermayer <michaelni@gmx.at>
(cherry picked from commit 970c8df73528659925819dec31c4c8c0887f0321)

Conflicts:
	libavcodec/mpeg12.c