Files in build directory without corresponding sources should be reported as warnings/errors

[euclidianAce]

Consider the following sequence of events:

• user has the following project:

src/
   foo.tl
   bar.tl
build/
   foo.lua
   bar.lua

• user renames bar.tl -> baz.tl and rebuilds resulting in:

src/
   foo.tl
   baz.tl
build/
   foo.lua
   bar.lua
   baz.lua

If the user has tests or other random files that require the compiledbar module, they could still work, and are likely to have subtle errors caused by this.

We should report that a file was found in the build_dir that was not expected and maybe add a flag to purge the build_dir of any unexpected files