Various fixes for deRPC.
- If an array type is artificially rescued, it should rescue its component type.
- Don't generate bad RPC proxy code if the legacy type-elision flag is set.
- Correctly handle CustomFieldSerializers that write null Strings.

Patch by: bobv
Review by: jgw (desk)

git-svn-id: https://google-web-toolkit.googlecode.com/svn/trunk@6323 8db76d5a-ed1c-0410-87a9-c151d255dfc7