log and diff family: honor config even from subdirectories

log and diff family: honor config even from subdirectories

There currently is an unfortunate circular dependency between
what init_revisions (the command line revision specification
parser) does and setting up the log and diff options.  The
function uses setup_git_directory() to find the root of the
project relative to the current directory and calls diff_setup()
to prepare diff generation.  However, some of the things that
diff_setup() does needs to depend on the configuration variable,
which needs to be read after setup_git_directory() is called.

This patch is a low impact workaround.  It first lets
init_revisions() to run and do its thing, then uses git_config()
and diff_setup() after it returns, so that configuration
variables that affects the diff operation can be used from
subdirectories.

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