Improve error message for missing local pod. Closes #323.

lib/cocoapods/local_pod.rb

@@ -223,7 +223,11 @@ module Pod
     end
 
     def expanded_paths(patterns, options = {})
-      raise Informative, "[Local Pod] Attempt to resolve paths for non existent pod." unless exists?
+      unless exists?
+        raise Informative, "[Local Pod] Attempt to resolve paths for nonexistent pod `#{@specification}'.\n" \
+                           "\tPatterns: #{patterns.inspect}\n" \
+                           "\t Options: #{options.inspect}"
+      end
 
       patterns = [ patterns ] if patterns.is_a? String
       patterns.map do |pattern|