Reverse previous workaround for pthreads lib having GC2 suffix - that
is actually normal; patch should instead go into x264 to make it ignore
the presence of a local pthread lib under cygwin when doing configure tests.

Contribs: take libebml and libmatroska from released versions... Way easier to not compile it everytime.

Ignore directories in --sub-autodetect-path that match the directory
of the current file (But it does not works with symbolic links).

Fixed an overflow when more than MAX_SUBTITLE_FILES are detected.
Fixed a bunch of memory leaks.
Fixed removing sub/idx pair. (sizeof() != strlen on char*)
Clean up/Simplify (asprintf/calloc are usefull)
Cosmetics

selected one with --sub-file

 - as a standalone file
 - as a kind of subtitle (even if it is a video track).
CD-G disk are not supported.

Please, report any file incorrectly decoded. (I have 0 sample with
circular scrolling)

In subtitle_Detect, do not add as a subtitle the file for which we
are doing the detection.
 (subtitle_Detect("file.sub") returned "file.sub")

Re-enables media library.
Fixes #1047 (nth attempt).

This means ICMP errors will be ignored, which is a Bad Idea.
But people are likely to complain about how it breaks their setup if we
don't ignore ICMP anyway.

These are not confidential, and fairly slow to compute.
(This is much simpler than caching them to disk, and more
 portable-app-friendly)