Removed dead global initializer code.
Removed TODO-riddled DtoInitializer only used in DtoVarDeclaration.
Refactoring-only part of DtoConstExpInit fix.
Be more lenient with initializer type mismatch; zext as necessary.

The integer initializer width mismatch issue should really be
fixed in the frontend, but is related to forward referencing
and thus hard to track down.

Also fixes an unlisted regression since the 2.061 merge, where
there would be a const(char*) vs. immutable(char*) mismatch
reported for some string constants.

GitHub: Fixes #378.
Merge pull request #379 from klickverbot/initializer-type-mismatch

Fix initializer type mismatch crash