cat: replace match.bad() monkey patching with match.badmatch()
No known issues with the previous code since it restored the original method,
but this is cleaner.
#require symlink
http://mercurial.selenic.com/bts/issue1438
$ hg init
$ ln -s foo link
$ hg add link
$ hg ci -mbad link
$ hg rm link
$ hg ci -mok
$ hg diff -g -r 0:1 > bad.patch
$ hg up 0
1 files updated, 0 files merged, 0 files removed, 0 files unresolved
$ hg import --no-commit bad.patch
applying bad.patch
$ hg status
R link
? bad.patch