Allows drush make to completely overwrite existing directories.
Merge pull request #873 from drush-ops/allow-overwrite

Allows drush make to completely overwrite existing directories.
Fix #886. Fatal error: Call to undefined function drush_module_exists() on test-run
Fix #879. Cater to older versions of Drush on a remote server when doing a user-login
Minor - reference the affected version, not the one before.
Change http to https. Progress on #894.
Fix reference to unknown variable in release_info engine.
Allow engines to live in lib/. Clean up, remove unneeded complexity.
Merge pull request #900 from jonhattan/engines-in-lib

Allow engines to live in lib/
Fix reference to unknown variable in release_info engine (2nd take).