Manual memory management in D2

[Francisco Almeida]

Replacing delete or forbidding it in detriment of a safer alternative
function indeed makes sense when compiling in the SafeD language subset.
However, the delete operation has a well defined role in "unsafe" D.
The most advantageous would be adding clear() as well as a possible
"destroy()" function, but keeping the delete operation legal, and forbid
it in SafeD mode only.