armv6: vp8: use explicit labels in motion compensation asm

The integrated arm assembler in clang-503.0.38 (Xcode-5.1) fails
to assemble a branch to 'label + offset' in thumb mode.
doc: Point to the correct, actually maintained gas-preprocessor repo

Signed-off-by: Martin Storsjö <martin@martin.st>
http: Properly initialize icy headers string

The icy_metadata_headers string never gets initialized, so,
during the first call to av_strlcatf() in parse_icy(),
strlen() will be called on a pointer to uninitialized memory.
At best this causes some garbage data to be left at the
start of the string.

By initializing icy_metadata_headers to the empty string, the
first call to strlen() will always return 0, so that data is
appended from the start of the string.

Signed-off-by: Luca Barbato <lu_zero@gentoo.org>
avconv: Match stream id

Quite useful to select by pid in MPEG-TS.
Prepare for 11_alpha1 Release