difftool: print list of valid tools with '--tool-help'th/difftool-diffall

Since bc7a96a (mergetool--lib: Refactor tools into separate files,
2011-08-18), it is possible to add a new diff tool by creating a simple
script in the '$(git --exec-path)/mergetools' directory.  Updating the
difftool help text is still a manual process, and the documentation can
easily go out of sync.

Teach the command to read the list of valid tools from the 'mergetools'
directory, determine which of them are actually installed and then print
them for the user when the '--tool-help' option is given.

Signed-off-by: Tim Henigan <tim.henigan@gmail.com>
Signed-off-by: Junio C Hamano <gitster@pobox.com>

0 files changed, 0 insertions, 0 deletions