If you call Revert modification on a single file, it takes a long time on a big
repository. To reproduce:
Running with hg 0.9.3 on OpenSoalris b78:

- take repository from
http://deadlock.netbeans.org/hudson/job/hgimport/lastSuccessfulBuild/artifact/apisupportx/hgimport/out/main.tar.gz
- untar with gtar
- run hg update to populate the working dir
- Edit and save
~/work/main/o.o.util/src/org/netbeans/modules/openide/util/AWTBridge.java

- run:
$ time hg revert --repository ~/work/main --rev 0
~/work/main/o.o.util/src/org/netbeans/modules/openide/util/AWTBridge.java

real    0m59.899s
user    0m27.126s
sys     0m3.109s