fix documentation detection with excess spacing

Previously we'd not take trailing spaces after the last argument into
account and prevent `(... SUBDIR foo    )` from matching. The regex now
gobbles up trailing spaces.
Added a test case with super excessive spacing to make sure this works.
Also adjusted the manpage fixture to employ fairly excessive spacing and
make sure space matching works as well for manpages.

CCMAIL: andrius@stikonas.eu