auto merge of #5155 : bstrie/rust/dedrop, r=pcwalton

This removes all but 6 uses of `drop {}` from the entire codebase. Removing any of the remaining uses causes various non-trivial bugs; I'll start reporting them once this gets merged.

src/libsyntax/parse/parser.rs

@@ -245,7 +245,11 @@ pub struct Parser {
     /// Used to determine the path to externally loaded source files
     mod_path_stack: @mut ~[~str],
 
-    drop {} /* do not copy the parser; its state is tied to outside state */
+}
+
+impl Drop for Parser {
+    /* do not copy the parser; its state is tied to outside state */
+    fn finalize(&self) {}
 }
 
 pub impl Parser {