Make util.find_exe alway returns existing file, fixing
issue1459
It seems like the old behaviour with different handling for commands with and
without path was intended, but I think this behaviour of util.find_exe is
better:
* Always returns existing file
* or None if command not found - no default
* Windows: Returned file thus always ends with extension from PATHEXT
This fixes http://www.selenic.com/mercurial/bts/
issue1459. The change might
fix other unintended behaviour too.
test-merge-tools
Some tests of merge-tools configuration and selection, mostly excercising
filemerge.py