Added String support to Collecting.
Added feature imports for implicit conversion and higher kinds in main code to eliminate feature warnings.
Removed the use of postfix feature in WebBrowser.scala.
Added feature imports to test code to reduce compiler warnings, and fixed some easy warnings.
First batch of changing mixin to import in test codes.
Second batch of changing mixin to import in test codes.
Merge branch 'feature-warning' of https://github.com/cheeseng/scalatest into 2.1.x