Send error during base.js init as string.

Currently, the error object gets interpreted as an options config object, and the
actual error message gets discarded. Casting it to a string preserves the error name
and message.

r2/r2/public/static/js/base.js

@@ -127,6 +127,6 @@ $(function() {
         r.newsletter.ui.init()
         r.cachePoisoning.init()
     } catch (err) {
-        r.sendError('Error during base.js init', err)
+        r.sendError('Error during base.js init', err.toString());
     }
 })