Refactor a handful of stuff in the metadata encoder.

Author: msullivan

src/librustc/metadata/common.rs

@@ -179,6 +179,8 @@ pub static tag_mod_child: uint = 0x7e;
 pub static tag_misc_info: uint = 0x7f;
 pub static tag_misc_info_crate_items: uint = 0x80;
 
+pub static tag_item_method_provided_source: uint = 0x81;
+
 pub struct LinkMeta {
     name: @str,
     vers: @str,