Reading services on Mac is very slow

Currently Puppet runs `plutil -convert xml1` on EVERY plist it encounters because it has no way of supporting binary plist files. This occurs even if the plist is a text file.

Speed up reading plists so it doesn't take 30 seconds to do so. The most promising approach to this is to first try reading the plist file as text, and if that fails (which happens immediately with binary plists) pipe it through plutil.

Measurements demonstrating that this gives significant performance improvements are attached to PUP-1455.