UglifyJs requires a '-' to use STDIN

cite: https://github.com/mishoo/UglifyJS2
  If you want to read from STDIN instead, pass a single dash instead of input files.
Merge pull request #157 from zeroasterisk/master

minor correction for UglifyJS
Cleaned up the test plugin ini file
Added helper test for targets from a plugin ini
Only loading the plugin when tests require it
Merge remote-tracking branch 'upstream/master'