test-merge-tool: Make sure no hgmerge can be found in $PATH
The merge tool selecting algorithm is hardcoded to look for hgmerge in $PATH
before it falls back to use internal merge. This fixes the test for this
fallback to be tolerant to existing hgmerges.
adding base
foo/renamed
renamed
bar/renamed
renamed
baz
.hg/patches/baz
% test patch being renamed before committed