Interactive editor tests for commit-msg hook

Interactive editor tests for commit-msg hook

Supplement the existing tests for the commit-msg hook (which all use
"git commit -m") with tests which use an interactive editor (no -m
switch) to ensure that all code paths get tested.

At the same time the quoting of some of the existing tests is changed
to conform to Junio's recommendations for test style (single quotes
used around the test unless there is a compelling reason not to, and
the opening quote on the same line as the test_expect and the closing
quote in column 1).

Signed-off-by: Wincent Colaiuta <win@wincent.com>
Signed-off-by: Junio C Hamano <gitster@pobox.com>