doc: document aresample:first_pts

Documentation copied from asyncts, the options are supposed to do
the same thing. If not please submit a testcase where they differ
so we can fix it.

Disscussed-with: saste on IRC
Signed-off-by: Michael Niedermayer <michaelni@gmx.at>
avcodec/x86/cabac: workaround llvm 4.2.1 bug

x86_64 is affected by this too
Fixes Ticket2156

Signed-off-by: Michael Niedermayer <michaelni@gmx.at>