t7610-mergetool: add test cases for mergetool.writeToTemp
t7610-mergetool: add test cases for mergetool.writeToTemp

Add tests to ensure that filenames start with "./" when
mergetool.writeToTemp is false and do not start with "./" when
mergetool.writeToTemp is true.

Signed-off-by: David Aguilar <9de348c050f7cd1ca590883733c4e531ce610bf4@gmail.com>
Signed-off-by: Junio C Hamano <a6723cc3f76163bf7adb636a73ac3b0ceb3e6b9b@pobox.com>

destenson/git,destenson/git,destenson/git,destenson/git,destenson/git,destenson/git,destenson/git,destenson/git