[PATCH] Don't update sps if they are only repeated

[PATCH] Don't update sps if they are only repeated

This is an attempt to improve the mitigations from #365 and #366 and picks up an idea I described at #345:

> One way would be just to look at the pointers of the SPS (fast and easy, but
> may reject more than required), or investigate if the SPS used for the image
> generations are "compatible".

This changes do exactly this: It (very conservativly) checks if the old and new sps have
identical information -- except the reference picture set, which I believe is supposed
to be updated by new sps'). If they are basically identical, the old sps will be
used instead of the new one, (of course, reference image set is updated from the new one)

I'm using standalone operator== and helper functions to avoid changing ABI of the library;
if an ABI bump would be done, of course this should go to the respective classes.

Gbp-Pq: Name recycle_sps_if_possible.patch