test-tool: show tool list on error
Before we switched to one big test-tool binary, if you
forgot the name of a tool, you could use tab-completion in
the shell to get a hint. But these days, all you get is:
$ t/helper/test-tool approxidate
fatal: There is no test named 'approxidate'
and you're stuck reading the source code to find it. Let's
print a list of the available tools in this case.
Signed-off-by: Jeff King <peff@peff.net>
Reviewed-by: Derrick Stolee <dstolee@microsoft.com>
Signed-off-by: Junio C Hamano <gitster@pobox.com>