revset: add matchany() to construct OR expression from a list of specs
This will allow us to optimize "-rREV1 -rREV2 ..." command-line options.
# The 9diff extdiff command generates diff(1) compatible output
# suitable for use with the plumber(4).
[extensions]
extdiff =
[extdiff]
9diff = /bin/mercurial/9diff -cm $parent $child $root