grc: allow set_min_output_buffer on any blocks that have output ports
grc: portability fix for older grc files that have missing affinity and minoutbuf keys
grc: checks for virtual/pad source/sink and ignores them for affinity and buffer size fields.
Merge branch 'master' of git.gnuradio.org:gnuradio
build: better fix for finding and handling ICE.