Issue 6545 - [CTFE] Hard-coded array operations not yet supported

Refactor array op generation and always generate a D version of the array operation.  In the interpreter, if a FuncDeclaration with no body is encoutered, use the D version if it is an array operation.

Having the bodies available also opens up opportunities for inlining, but they are not explored with this patch.

http://d.puremagic.com/issues/show_bug.cgi?id=6545