Merge default into stable for the 1.6 code freeze

revset: improve help on strings

tests: extend revset test

merge: sort arguments to stabilize the ancestor search

merge: improve merge with ancestor message

ui: ignore EIO in write_err Hgs signal handler will catch the signal for example if the terminal hg is running in is closed. That will make it try to warn that it was 'killed', but that might fail with EIO and cause hg to exit with an unhandled exception. Normally nobody cares, but system error handlers such as Fedoras abrt will notice and report https://bugzilla.redhat.com/show_bug.cgi?id=596594 .

http push: break infinite recursion on failure with Python 2.6.5 (issue2179) Python 2.6.5 will keep resetting the retry count on redirects, for example when the server returns 401 on failing auth (like google code currently does). We stop the endless recursion by not resetting the count. http://bugs.python.org/issue3819 introduced the regression with Python 2.6.5. http://bugs.python.org/issue8797 discusses a fix which might make it to 2.6.6 and 2.7.0.