Add a helper to get the right values from the RTSP code

Calls to aout_PrepareFormat where missing.

 It fixes segfaults in src/input/stream.c (at least) when demuxers
overflow int64_t seek position, and avoid testing for negative values
everywhere.
 stream_Tell() and stream_Size() still returns signed values as too much code
depend on it.

They were dead long enough.

This codec wasn't good.
It didn't work on SIPR correctly in all cases.
The code had lots of warnings.
The philosophy of it sucks (opening dlls...)
It didn't work on non-standard architecture.

We don't use the TTL value in SDP anymore, but we still do in RTSP

This has been broken for sure since 1.0, most probably nuch earlier.

I AM in Ur FFmpeg, br34King Ur codez :

It seem to not work because of cross-compilation. It seems to call directly pkg-config with no way of overriding it.
--disable-avs-input --disable-lavf-input --disable-ffms-input --disable-mp4-output

Saving pointers in the cache makes no sense. In this case, we only want
to know that the plugin must be preloaded so that the configuration item
callback works from the preference dialog.

This can't be useful anymore, otherwise connections would always
fail... and it was preventing VLC from prompting the user for
authentication credentials (untested).

a templated helper. The holder variables are not otherwise used so a
pointer to the (virtual) interface classes works fine.