obscache: directly allocate zeroed bytearray This is much faster that incrementally appending to it. On mozilla central without obsolescence markers this move full cache building from 0.3s to nothing visible.

syntax: re
/figures/[^/]+\.png$
^html/
\.pyc$
~$
\.swp$
\.orig$
\.rej$
\.err$
^tests/easy_run.sh$
^build/
^dist/
^MANIFEST$
^docs/tutorials/.*\.rst$
\.ico$
tests/\.testtimes