swift234

Mangle operator fixity and tuple variadicity.

Tweak the mangling rules to fix some collisions I found:

- Mangle variadic tuples with a lowercase 't' to distinguish them from nonvariadic tuples with a slice as their final element.
- Mangle the fixity of operators using 'op' for prefix, 'oP' for postfix, and 'oi' for infix, so that operator declarations that differ only in fixity can coexist.

While we're here, 'Slice' seems worthy of a standard substitution, so mangle it to 'Sa'.

This fixes <rdar://problem/13757744> and <rdar://problem/13757750>.

Swift SVN r4965