Compatibility to Julia v0.4

Requires Compat.jl
In all my upcoming pull requests, there's a "using Compat" included in the file. Probably that's not the way to do it (I guess there should be a require Compat somewhere when loading the package, rather than a using in every file), but it won't work unless I do this on my machine.

All of this is tested to run with Light Table 0.7.1, Juno 0.9.1, Julia 0.9.2 plugins using both Julia versions 0.3.2 and 0.4.0  
Would be good to indent to `raise(` here as well