Commit Briefs
vac: handle mid
R=rsc CC=plan9port.codebot http://codereview.appspot.com/5451114
vacfs: fix segfault when no prefix specified
R=rsc CC=plan9port.codebot http://codereview.appspot.com/5451052
vac: debug prints
R=rsc CC=codebot http://codereview.appspot.com/816041
vac: add -a and -x flags
Thanks to Michael Kaminsky for the suggestion.