Improve a bit ikiwiki detection (#1824)

* Improve a bit ikiwiki detection

This can be verified
[here](http://blog.spang.cc/posts/hledger_rocks_my_world/). Apparently
people may put ikiwiki in the good ol' `/cgi-bin` folder instead of the
root of their website. This makes sense, since ikiwiki is a big pile of
Perl.

* Fix a typo