Make sure to have both upper and mixed case symbols in SYMBOL_VECTOR

It was assumed that the syntax FOO/Foo=PROCEDURE would create both an
upper case and mixed case symbol in the GST.  Not so, it requires
having both FOO/Foo=PROCEDURE (to create the upper case alias) and
Foo=PROCEDURE (to create the mixed case slot).

We make sure that any symbol always occupies two slots (even those
that don't exist) by filling up with SPARE when necessary.  That will
assure that any changes will still have the same symbols in the same
slots no matter what (save a complete rewrite of the ordinals files).

Reviewed-by: Rich Salz <rsalz@openssl.org>