Tidy up error messages.
S11N: Add support for serialization
S11N: add support for serializing instances of member classes.
S11N: tests
S11N: test: Fix MiscTest.compileRuntime for new serialization package.
S11N: Add the serialization tests to the LanguageSuite

This reverts commit ae947a66756619aa5d54a92e35a41cb63ef93245.
Attempted fix for #1868, which didn't work, but it seems likely we'll need this for other reasons...
S11N: Prevent serializing of instances with unitialized late attributes.
Update test for serialization of instances with unitialized late attributes.