windows: expand environment vars in find_exe
This allows us to use ${ProgramFiles} in our [merge-tools] sections so
we can provide locale safe program paths.
#!/bin/sh
#
hg init foo
cd foo
touch a
unset HGUSER
echo "[ui]" >> .hg/hgrc
echo "username= foo" >> .hg/hgrc
echo " bar1" >> .hg/hgrc
hg ci -Am m
rm .hg/hgrc
HGUSER=`(echo foo; echo bar2)` hg ci -Am m
hg ci -Am m -u "`(echo foo; echo bar3)`"
true