auto merge of #6833 : fdr/rust/fix-warnings, r=Aatch

Fix a laundry list of warnings involving unused imports that glutted
up compilation output.  There are more, but there seems to be some
false positives (where 'remedy' appears to break the build), but this
particular set of fixes seems safe.

src/libsyntax/parse/parser.rs

@@ -92,7 +92,6 @@ use parse::{new_sub_parser_from_file, next_node_id, ParseSess};
 use opt_vec;
 use opt_vec::OptVec;
 
-use core::char;
 use core::either::Either;
 use core::either;
 use core::hashmap::HashSet;