Clean up app.start tests
Raise on unknown dependencies for deps.get and deps.update
Ensure File.cp_r/3 respects trailing / in sources
Ensure doc_line resets algebra formatting line buffer, closes #2014
Remove pre-copying of dev dependencies

The current code was copying manifests but they got
recent access times which caused bugs. Also, a dependency
can have different results depending on each dependencies
are available and which are not, so simply copying the
compiled dep can lead to weird errors.
Document inlined functions are BIFs
Improve contracts for Dict

1. Functions like merge/2 and equal?/2 are only polymorphic in the
Dict module. Implementations of the Dict module only need to
care about equality and merging of the same types.

2. take/2, drop/2 and split/2 accept any Enum as argument.