[REG2.064a] Issue 10734 - Assertion failure: '0' on line 1546 in file 'cast.c'

http://d.puremagic.com/issues/show_bug.cgi?id=10734

It's a 2.064a regression introduced by 'improveDefArgs' change
commit: a711eb6b499ca85b7cfa4e758d9e968fef8d315f

Just to be sure, not only the type comparison in `AddrExp::castTo`, I'd also fix others in `cast.c`. Because it is a central for expression type conversion.