Getting close to handling 300 declarations.

Memory usage contained with frequent forced fullGC() calls. EVAL now
called repeatedly on independent compile_dec1 calls. Also get more
diagnostic information so the interactive user can see what is being
compiled.

Only obstacle in most recent experiments is spurious HOL_ERR
exceptions that don't occur predictably. I assume these are a Poly/ML
bug, but it's certainly a bit of a worry.
Tidy up the EVAL example.  In theory all 356 declarations can compile.

In practice, I'm getting non-reproducible errors when I attempt to
build. I may try exporting intermediate results via save_thm, and
finishing the work off in a separate theory. I'd also be interested to
hear if a using a machine with more memory makes any difference.