Prevented test for defer attribute to match file name in src attribute; Added corresponding unit-test

The current test for defer attribute match the following:
`<script src="path/containing/defer-keyword.js"></script>`
I added a space character as a prefix to avoid matching a file path unexpectedly.
Support multiple targets in useminPrepare
Merge pull request #194 from dharFr/defer-false-positive

Prevented test for defer attribute to match file name in src attribute;
Merge pull request #206 from sorich87/usemin-prepare-multiple-targets

Support multiple targets in useminPrepare