Add expandMapping .extDot option. Closes gh-979.

* Can be 'first' or 'last' but defaults to 'first'.
extract util to grunt-legacy-util
Remove orphaned npm-issue-3958-workaround dep.
Empty string "ext" should strip extension. Closes gh-1087.
Update rimraf to latest version. Closes gh-1043.

* Ref gh-746
Better error in renameTask if task doesn't exist. Closes gh-1058.

* Also, instead of throwing an exception, just log the error message.
task.normalizeMultiTaskFiles now flattens nested "files" arrays. Closes gh-1034.
Update CHANGELOG
Bumping version to 0.4.3.