Avoid using "git-var -l" until it gets fixed.

Avoid using "git-var -l" until it gets fixed.

This is to be nicer to people with unusable GECOS field.

"git-var -l" is currently broken in that when used by a user who
does not have a usable GECOS field and has not corrected it by
exporting GIT_COMMITTER_NAME environment variable it dies when
it tries to output GIT_COMMITTER_IDENT (same thing for AUTHOR).

"git-pull" used "git-var -l" only because it needed to get a
configuration variable before "git-repo-config --get" was
introduced.  Use the latter tool designed exactly for this
purpose.

"git-sh-setup" used "git-var GIT_AUTHOR_IDENT" without actually
wanting to use its value.  The only purpose was to cause the
command to check and barf if the repository format version
recorded in the $GIT_DIR/config file is too new for us to deal
with correctly.  Instead, use "repo-config --get" on a random
property and see if it die()s, and check if the exit status is
128 (comes from die -- missing variable is reported with exit
status 1, so we can tell that case apart).

Signed-off-by: Junio C Hamano <junkio@cox.net>