configure: Separate "ln" command line arguments

This is more compatible and not more complicated.
configure: Identify icc compiler with a less ambiguous pattern
vorbisdec: cosmetics: rename variable avccontext to avctx

This is consistent with the rest of libavcodec.
vorbisenc: cosmetics: rename variable avccontext to avctx

This is consistent with the rest of libavcodec.
libschroedinger: cosmetics: rename variable avccontext to avctx

This is consistent with the rest of libavcodec.
cmdutils: only use libavresample when it is enabled

avprobe and avserver use cmdutils and do not strictly require libavresample.
avconv: remove an unused variable