FIX: In development mode on OSX, plugin stylesheets were not reloading

It seems to be due to symlinks in the plugins folder. Watching
the individual plugins seems to fix the issue rather than the entire
plugin folder.

lib/stylesheet/watcher.rb

@@ -10,10 +10,20 @@ module Stylesheet
     end
 
     def initialize(paths)
-      @paths = paths || ["app/assets/stylesheets", "plugins"]
+      @paths = paths || Watcher.default_paths
       @queue = Queue.new
     end
 
+    def self.default_paths
+      return @default_paths if @default_paths
+
+      @default_paths = ["app/assets/stylesheets"]
+      Discourse.plugins.each do |p|
+        @default_paths << File.dirname(p.path).sub(Rails.root.to_s, '').sub(/^\//, '')
+      end
+      @default_paths
+    end
+
     def start
 
       Thread.new do