Merge pull request #61 from ihnorton/master

Update helpful message on (load) failure
Fix for this error:
ERROR: function warn_once does not accept named arguments
warn_once has the following signature:
in utils.jl: function warn_once(msg::String...)
Merge pull request #62 from bass3m/master

Fix for "ERROR: function warn_once does not accept named arguments"
Cache dependencies during install macro