src: fix mismatched delete[] in src/node_file.cc

src: fix mismatched delete[] in src/node_file.cc

Fix a bad delete of a pointer that was allocated with placement new.
Casting the pointer was not the right solution because there was at
least one non-placement new constructor call.

This commit rewrites FSReqWrap to be more explicit about ownership of
the auxiliary data and removes a number of egregious const_casts.
The ASYNC_DEST_CALL macro also gets significantly slimmed down.

PR-URL: https://github.com/iojs/io.js/pull/1092
Reviewed-By: Fedor Indutny <fedor@indutny.com>