The BIF was not returning an IntervalVal which has an overriden
ValDescribe() method that allows for prettier printing like "6.0 secs"
instead of just "6.0".
This also installs symlinks from "zeek" and "bro-config" to a wrapper
script that prints a deprecation warning.
The btests pass, but this is still WIP. broctl renaming is still
missing.
#239