libsyntax: De-`@mut` `name_idx`
libsyntax: De-`@mut` the path in the AST mapping context
libsyntax: De-`@mut` (and de-`@`) the AST mapping context
libsyntax: De-`@mut` the interner map
libsyntax: De-`@mut` `SCTable::table`
libsyntax: De-`@mut` `SCTable::mark_memo`
libsyntax: De-`@mut` `SCTable::rename_memo`
libsyntax: De-`@mut` `SCTable`
libsyntax: De-`@mut` `BlockInfo::pending_renames`
libsyntax: Remove an unnecessary `@mut io::Reader`
libsyntax: Correctly de-`@mut` the pretty printer writer
libsyntax: De-`@mut` `FileMap::lines`
libsyntax: De-`@mut` `FileMap::multibyte_chars`
libsyntax: De-`@mut` `CodeMap::files`
libsyntax: De-`@mut` `Interner::vect`
libsyntax: De-`@mut` (and de-`@`) `Printer::print_stack`
libsyntax: De-`@mut` `ps::boxes`
librustc: Eliminate an unnecessary `@mut` in pretty printing.

This removes all `@mut` from `librustc` and `libsyntax`.
librustpkg: De-`@mut` `rustpkg`
librustdoc: De-`@mut` `librustdoc`