two patches for better jc1 error handling

[Per Bothner]

The first patch is needed to recover from bad assignments
like:
   String x = 30;

The second patch is needed to catch errors like:
   String x = 0;
There are other ways to solve the problem, but I don't see
any reason for a special case for 0 so I removed it.

Fixing this triggers a few problems in libjava where
0 is assigned to RawData fields.  The ones I've come
across so far are in gnu.gcj.xlib.  Before I check this
patch in, I'll fix those (and run the testsuite).
-- 
	--Per Bothner
per@bothner.com   http://www.bothner.com/per/