Workaround bugs in Proxy serialization

[Andrew Haley]

For those of you that may be wondering what this was all about, there
is an excellent RMI tutoral at http://java.sun.com/docs/books/tutorial/rmi/TOC.html

This example worked with gcj as long as Sun's rmiregistry was being
sued, but not with grmiregistry, which segafulted.  The changes I made
in gcj's serialization code mean that we have interoperability between
Sun's RMI and gcj's, in both client-server directions.

I haven't tried anything more elaborate than this simple test, though.

Andrew.