Fixed and improved text.csv

As suggested by enami (http://chaton.practical-scheme.net/gauche/a/2013/06/01#entry-51a991df-25317)
Exit abnormally when any submake fails

Failure of recursively called make has been ignored if it is
in the for loop and not for the last item.  That masks build
failure we need to watch.
Build dependency fix
Add const modifier to read-only tables
Fixed regexp backreference parser bug
Comment grammatical fix
Small fix and cosmetic changes in text.csv
Better error message in vm-build-insn
Improved performance of csv reader

by avoiding using with-input-from-port; it allocates a closure
and a handler chain, which happens at *every row*.
Make eof-object inlined
A pass5 optimization
Cosmetic changes
Support 'export' form without *.sci file

This is an internal matter---for precompiled extension modules, export
form will be included in *.sci file as a part of define-module form,
so the C part doesn't need to worry about exporting.  However, to build
the Gauche core, where we don't generate *.sci files, we do need exporting
in the C init function.
Splitted VM code generation API inoto gauche.vm.code module
Small stylistic changes
Fix to return the result from %mtqueue-overflow?

This also adds test cases for enqueue-unique! and queue-push-unique!
ChangeLog addition for the last commit
Added vm-insn-size in gauche.vm.insn
Experimentally added precompile time optimization
Flushed obsoleted code