Add spaces around the :: in a use of $crate:: to not hit regex for crate::

Hacks on top of hacks, to make the 0.2 branch deal with old tooling.

Author: joshtriplett

src/macros.rs

@@ -270,7 +270,8 @@ macro_rules! c_enum {
 
     // Use a specific type if provided, otherwise default to `c_uint`
     (@ty $repr:ty) => { $repr };
-    (@ty) => { $crate::c_uint };
+    // This has a space after `$crate` to avoid matching the regex for `crate::`.
+    (@ty) => { $crate :: c_uint };
 }
 
 // This is a pretty horrible hack to allow us to conditionally mark some functions as 'const',