merge: fix a copy detection bug (issue672) When merging rev1 and rev2, we want to search for copies that happened in rev1 but not in rev2 and vice-versa. We were starting the search at rev1/rev2 and then going back, stopping as soon as we reached the revno of the ancestor, but that can miss some cases (see the new test-issue672). Now we calculate the revisions that are ancestors of rev1 or rev2 (but not both) and make sure the search doesn't stop too early. Simplified test provided by mpm, based on a test case provided by Edward Lee.

adding bar
adding foo
adding bomb
adding a.c
adding dir/a.o
adding dir/b.o
M dir/b.o
! a.c
! dir/a.o
? .hgignore
a.c: unsupported file type (type is fifo)
! a.c
# test absolute path through symlink outside repo
A f
# try symlink outside repo to file inside
abort: ../z not under root
# try cloning symlink in a subdir
1. commit a symlink
? a/b/c/demo
adding a/b/c/demo
2. clone it
1 files updated, 0 files merged, 0 files removed, 0 files unresolved