comp: allowed the declaration of pure fn's in native mods

This is especially useful for the native calls in std::math

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Author: boggle

src/comp/middle/typeck.rs

@@ -1501,6 +1501,7 @@ fn require_pure_call(ccx: @crate_ctxt, caller_purity: ast::purity,
       ast::pure_fn. {
         alt ccx.tcx.def_map.find(callee.id) {
           some(ast::def_fn(_, ast::pure_fn.)) { ret; }
+          some(ast::def_native_fn(_, ast::pure_fn.)) { ret; }
           _ {
             ccx.tcx.sess.span_err
                 (sp, "pure function calls function not known to be pure");

src/comp/syntax/parse/parser.rs

@@ -1975,6 +1975,9 @@ fn parse_native_item(p: parser, attrs: [ast::attribute]) ->
         ret parse_item_native_type(p, attrs);
     } else if eat_word(p, "fn") {
         ret parse_item_native_fn(p, attrs, ast::impure_fn);
+    } else if eat_word(p, "pure") {
+        expect_word(p, "fn");
+        ret parse_item_native_fn(p, attrs, ast::pure_fn);
     } else if eat_word(p, "unsafe") {
         expect_word(p, "fn");
         ret parse_item_native_fn(p, attrs, ast::unsafe_fn);