Hacking tweaks

Three issues I've bumped into here:

* Just `./configure --skype=1 && make` doesn't produce a testable setup and might be especially confusing if bitlbee will keep loading skype.so from /usr/lib (which it seem to be configured to do by default) instead of development version, hence the mention of the thing in HACKING.

* Failing tests aren't repeatable as they leave skyped hanging, hence try..finally wrapping.

* Timing-out (basically anything unexpected there) tests don't seem to produce any useful output, hence pexpect.log alongside skyped.log.

As all of these seem to be purely dev-setup related, mashed these together into one PR.