Emulate System.getProperty(key, default) by always returning the
default. This method is commonly used by parsers for establishing the
newline character, so including this makes it possible to port such code
to GWT.

Review at http://gwt-code-reviews.appspot.com/1654803


git-svn-id: https://google-web-toolkit.googlecode.com/svn/trunk@10900 8db76d5a-ed1c-0410-87a9-c151d255dfc7