config: clarify meaning of command line scoping

config: clarify meaning of command line scoping

CONFIG_SCOPE_CMDLINE is generally used in the code to refer to config
values passed in via the -c option.  Options passed in using this
mechanism share similar scoping characteristics with the --file and
--blob options of the 'config' command, namely that they are only in use
for that single invocation of git, and that they supersede the normal
system/global/local hierarchy.  This patch introduces
CONFIG_SCOPE_COMMAND to reflect this new idea, which also makes
CONFIG_SCOPE_CMDLINE redundant.

Signed-off-by: Matthew Rogers <mattr94@gmail.com>
Signed-off-by: Junio C Hamano <gitster@pobox.com>