Merge pull request #1433 from ericmj/mix-deps-check

Rename mix flag --no-check -> --no-deps-check, document it and use it everywhere
Document that on_definition can only be a function, closes #1431
Update CHANGELOG
No need to define a new compilation error
Fixed typos and formatting issues in Mix.Tasks.CompileElixir
Fixed doc typos in Mix.Tasks.Compile.*
Merge pull request #1438 from jwarwick/mix_tasks

Fixed doc typos in Mix.Tasks.Compile.*
Add @protocol attribute to defimpl
Merge pull request #1439 from meh/protocol

Add @protocol attribute to defimpl
Ensure __impl__ follows the same convention as other dynamically generated info functions
Remove test at the wrong location
Improve docs for Mix.Deps
Check path deps to see if we should recompile

'mix compile' will check the manifest files' mtime of all mix path
dependencies - if they are newer then the local .compile.elixir file
we need to recompile.