Fixed an improper error message

Forgot to check that type=="string" before doing pattern matching on a field content.

Was triggered when version was provided as a string in a luarock.
Make the download command work with the file:// protocol
Merge branch 'master' of github.com:keplerproject/luarocks
Major updates, hopefully speeding up things.
Preload necessary rocks and rockspecs and create a local server.
Cache LuaSocket compilation for tests that need it.
Use LuaCov 0.4
Add Travis-CI badge to the README file
Merge pull request #200 from fab13n/master

Fixed an improper error message
Propagate failure of MD5 correctly. Closes #184.
Test environment improvements
More tests
Add named trees, as suggested by @Tieske, plus tests.
Fix some tests that only run locally.
Make default rocks_trees named as well.
Prioritize "scm" over "cvs". This was underspecified before.
Add check that will be used to ensure no rocks without licenses are uploaded.
Closes #202.