Updating to support new this.files property per gruntjs/grunt#606.

* this.files.forEach iterates over all src-dest file pairs.
* f.src.filter() warns on and removes possible invalid source files (in case the user set nonull), but doesn't fail the task.
* Uncaught exceptions will fail the task.
Updating to support grunt 0.4.0rc5 and publishing to npm.
Bumping version to 0.1.1rc6 and publishing to npm.

* Updating grunt/gruntplugin dependencies to rc6.
* Changing in-development grunt/gruntplugin dependency versions from tilde version ranges to specific versions.
multiple sourceMap
added tests for multiple sourcemaps in one definition
adding better error reporting