Emplace fixup

Just a little series of "trivial" fixups related to my recent emplace fix.

This does not change any existing behavior, or try to fix anything that is broken. It is only mostly cleanup, removing un-needed code, rewrite error messages as cleaner `format`, as well as reword them a teensy-bit

I did introduce a private template: `lvalueInit`, that returns a static `T.int`, as immutable, and reference-able. This is actually quite convenient, and avoids the creep of each function declaring its own local copy, just to memcpy.

Simpler to review each pull individually I think.

I'd rather these be fixed now, so I can tackle:
1. http://d.puremagic.com/issues/show_bug.cgi?id=10973
2. http://d.puremagic.com/issues/show_bug.cgi?id=10978
So as to reduce the noise in pulls that actually change things.