fix traceback of extdiff after a merge
- files that comes from a different branch are marked as modified
but aren't present in the original manifest
- add a testcase for extdiff and for regular diff
#!/bin/shmkdir acd ahg initecho foo > bhg add bhg ci -m "b" -d "1000000 0"chmod -w .hgcd ..hg clone a bchmod +w a/.hg # let test clean upcd bhg verify