libsyntax: Fix parsing of "loop unsafe".

It was getting misparsed as a label.

Author: pcwalton

src/libsyntax/parse/parser.rs

@@ -1600,7 +1600,7 @@ class parser {
 
     fn parse_loop_expr() -> @expr {
         let opt_ident;
-        if is_ident(self.token) {
+        if is_ident(self.token) && !self.is_any_keyword(copy self.token) {
             opt_ident = some(self.parse_ident());
             self.expect(token::COLON);
         } else {

src/test/run-pass/loop-unsafe.rs

@@ -0,0 +1,8 @@
+// Tests that "loop unsafe" isn't misparsed.
+
+fn main() {
+    loop unsafe {
+        io::println("Hello world!");
+    }
+}
+