Update fix "usrs" typo in lessc warning output

Enyo-DCO-1.1-Signed-Off-By: Ben Combee (ben.combee@lge.com)
Handle non-relative paths & alternate package.js files.

Fixes are needed for using latest Enyo minifier script with
on-device build scripts.

Enyo-DCO-1.1-Signed-Off-By: Ben Combee (ben.combee@lge.com)
Merge pull request #566 from enyojs/minifier-fix

Minifier fix