Make sys includes POSIX-compliant

We're using <sys/resources.h> in quassel.cpp for the backtrace generation
stuff. Documentation for that header indicates that <sys/time.h> shall also
be included (even though it doesn't seem to be needed for our usage).
Additionally, compiling started to fail in recent FreeBSD versions, because
we lacked the <sys/types.h> include, which seems to be mandated by POSIX
(but not on Linux, although it won't hurt to have it).

tl;dr: This should make Quassel compile on recent versions of FreeBSD again.