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
As opposed to plugins depending on a Bro source/build tree. This
required installing various Bro headers, BinPAC and it's headers,
bifcl, and Bro's custom CMake modules.