lavf: properly document the distinction between flags and ctx_flags
build: do not append $(FFLIBS-) to $(FFLIBS) if $(NAME) is not defined

Avoids including disabled library Makefiles.
Merge commit 'a738540366c9b114949b7914c0d08e2c28982cfb'

* commit 'a738540366c9b114949b7914c0d08e2c28982cfb':
  lavf: properly document the distinction between flags and ctx_flags

Merged-by: Michael Niedermayer <michaelni@gmx.at>
Merge commit '7e90133f6420b1c53652f972b9561600822881ee'

* commit '7e90133f6420b1c53652f972b9561600822881ee':
  build: do not append $(FFLIBS-) to $(FFLIBS) if $(NAME) is not defined

Conflicts:
	common.mak

See: efa95968317411179b0016af54745906029c2295
Merged-by: Michael Niedermayer <michaelni@gmx.at>
avutil/version: add FF_CONST_AVUTIL53

This will become "const" on the next major API version

Signed-off-by: Michael Niedermayer <michaelni@gmx.at>
avutil/fifo: delay addition of const from 78d3453c4a2efef9bc079e8f3458653beafcf990 until next major ABI bump

This unbreaks API, for example audacity has more build errors due to this

Signed-off-by: Michael Niedermayer <michaelni@gmx.at>
avutil/dict: delay addition of const from e12a73246d8ce7d0fc4036522688934e26de4bb1 until next major ABI bump

This unbreaks API

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