added documentation for settings: ENGINE_DEBUG, DOWNLOADER_DEBUG

--HG--
extra : convert_revision : svn%3Ab85faa78-f9eb-468e-a121-7cced6da292c%40721

scrapy/trunk/docs/ref/settings.rst

@@ -271,6 +271,15 @@ Default: ``True``
 
 Whether to collect depth stats.
 
+.. setting:: DOWNLOADER_DEBUG
+
+DOWNLOADER_DEBUG
+----------------
+
+Default: ``False``
+
+Whether to enable the Downloader debugging mode.
+
 .. setting:: DOWNLOADER_MIDDLEWARES
 
 DOWNLOADER_MIDDLEWARES
@@ -329,6 +338,15 @@ Default: ``180``
 
 The amount of time (in secs) that the downloader will wait before timing out.
 
+.. setting:: ENGINE_DEBUG
+
+ENGINE_DEBUG
+------------
+
+Default: ``False``
+
+Whether to enable the Scrapy Engine debugging mode.
+
 .. setting:: ENABLED_SPIDERS_FILE
 
 ENABLED_SPIDERS_FILE