debugdiscovery: small internal refactoring
The part of the code displaying statistic is made independant from the one
running the discovery. In the same do, the declaration of the discovery
function is a bit simplified.
#require emacs
$ emacs -q -no-site-file -batch -l $TESTDIR/../contrib/hg-test-mode.el \
> -f ert-run-tests-batch-and-exit
Running 1 tests (*) (glob)
passed 1/1 hg-test-mode--compilation-mode-support
Ran 1 tests, 1 results as expected (*) (glob)