tests/test-586

use internal merge tool when specified for a merge-pattern in hgrc

It is possible to specify in the hgrc file that one of the internal merge
tools (internal:fail, internal:local or internal:other) be used for
performing merges on files matching a given pattern. However, this setting
is not being acted upon (the merge tool is not found). This patch fixes that.

#!/bin/sh
# a test for issue586

hg init a
cd a
echo a > a
hg ci -Ama

hg init ../b
cd ../b
echo b > b
hg ci -Amb

hg pull -f ../a
hg merge
hg rm -f a
hg ci -Amc

hg st -A