This reverts commit b06a6ecadd.

- Crashes in providers lib when no providers in a namespace are bare
- Making sure bareness matches semantics; i.e. a bare provider is
  visible, a non-bare provider is hidden.

adding it results in ct test suites being compiled before they're
properly copied so changes made to suites between runs are not
reflected if a run fails before test dirs are copied

like `src_dirs`, `extra_src_dirs` are directories to be copied to
the `_build` dir and compiled. unlike `src_dirs` they are not added
to the .app specification

matching directory paths

run subsets of test suites

Also expose it in rebar_api

root project

get correct compile paths included in module info

`rebar.config` or via the `-c\--cover` flag given to the appropriate
task) from the `eunit` and `ct` tasks and add a `cover` task to
write coverage analysis to disk

`erl_first_files`

fixes #99

from run to run

`common_test` and `eunit` providers

compiles apps and eunit test files in a temporary dir (or a user
specified dir) and runs tests without leaving artifacts in the
source tree

automatically defines the 'TEST' macro if not already defined and
adds `test` to `src_dirs` to allow for eunit test files outside `src`