Do not let check_edown halt a build if init:get_plain_arguments() is empty

This may happen in case if rebar is used as a library.
Merge pull request #48 from proger/get_plain_arguments-fix

Do not let check_edown halt a build if init:get_plain_arguments() is empty
correct remove of globals on process DOWN
Merge pull request #49 from 0ctave/master

Correct remove of globals on process DOWN