Fix a couple of bugs in BigDecimal that were corrected in the
gwt-java-math project.

Public review at: http://gwt-code-reviews.appspot.com/153814/show

Patch by: jat, richard@zschech.net
Review by: rice


git-svn-id: https://google-web-toolkit.googlecode.com/svn/trunk@7644 8db76d5a-ed1c-0410-87a9-c151d255dfc7