Allegro CL modern mode compatibility

Nibbles wasn't usable on Allegro CL with modern mode enabled since nibbles creates symbols for function names explicitly in uppercase.

The functions for creating function name symbols have been updated to work regardless of case mode.

See: http://franz.com/support/documentation/8.2/doc/case.htm#creating-symbols-2

I ran into this bug when I found that my own project (cl-erlang-term) that use nibbles didn't build and run on ACL with modern mode.

See: http://common-lisp.net/project/cl-test-grid/library/cl-erlang-term.html