stripspace: respect repository config

stripspace: respect repository config

The way "git stripspace" reads the configuration was not quite
kosher, in that the code forgot to probe for a possibly existing
repository (note: stripspace is designed to be usable outside the
repository as well).  It read .git/config only when it was run from
the top-level of the working tree by accident.  A recent change
b9605bc4f2 ("config: only read .git/config from configured repos",
2016-09-12) stopped reading the repository-local configuration file
".git/config" unless the repository discovery process is done, so
that .git/config is never read even when run from the top-level,
exposing the old bug more.

When rebasing interactively with a commentChar defined in the
current repository's config, the help text at the bottom of the edit
script potentially used an incorrect comment character. This was not
only funny-looking, but also resulted in tons of warnings like this
one:

	Warning: the command isn't recognized in the following line
	 - #

Signed-off-by: Johannes Schindelin <johannes.schindelin@gmx.de>
Signed-off-by: Junio C Hamano <gitster@pobox.com>