configure: add settings for gitconfig, editor and pager
configure: add settings for gitconfig, editor and pager

Use the new GIT_PARSE_WITH_SET_MAKE_VAR macro to allow configuration
settings for ETC_GITCONFIG, DEFAULT_PAGER and DEFAULT_EDITOR.

Signed-off-by: Ben Walton <6f9de98cc1f3d6d6e7da9953ca2250e07ad38e43@artsci.utoronto.ca>
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