revlog: add "iscensored()" to revlog public API
The iscensored method will be used by the exchange layer to reject
nonconforming deltas involving censored revisions (and to produce
conforming deltas).
For background and broader design of the censorship feature, see:
http://mercurial.selenic.com/wiki/CensorPlan
# invalid filenames
test-add.t
test-init.t
test-clone.t
test-contrib.t
test-hgweb-raw.t
test-walk.t
# no sockets or fifos
test-hup.t
# no hardlinks
test-hardlinks.t
test-relink.t
# exec bit problems
test-convert-bzr-114.t
test-convert-bzr-directories.t
test-convert-bzr-merges.t
test-convert-bzr-treeroot.t
test-convert-darcs.t
test-merge-tools.t
# debugstate exec bit false positives
test-dirstate.t
test-filebranch.t
test-merge-remove.t