Fix the itruncalypse

I have to give credit to @nolta for a name that has kept me smiling all afternoon.

This tries to excise all mention in Base of `uint(LITERAL)` where `LITERAL` is 64 bits wide.  This builds on my 32-bit VM, but I'd like a human eye to go over this and make sure I'm not doing anything horrendously stupid here.
Thanks.