removed unused (and broken) prepend_callback Request method

--HG--
extra : convert_revision : svn%3Ab85faa78-f9eb-468e-a121-7cced6da292c%40728

scrapy/trunk/scrapy/contrib/history/scheduler.py

@@ -1,3 +1,7 @@
+"""
+WARNING: This Scheduler code is obsolete and needs to be rewritten 
+"""
+
 from datetime import datetime
 
 from twisted.internet import defer
@@ -90,6 +94,7 @@ class RulesScheduler(Scheduler):
 
         d = defer.Deferred()
         d.addCallbacks(callback, errback)
-        request.prepend_callback(d)
+        # prepend_callback Request method was removed (it never worked properly anyways) 
+        #request.prepend_callback(d)
 
         return request

scrapy/trunk/scrapy/http/request.py

@@ -58,14 +58,6 @@ class Request(object):
             return chain_deferred(self.deferred, callback)
         return self.deferred.addCallback(callback, *args, **kwargs)
 
-    def prepend_callback(self, func, *args, **kwargs):
-        if callable(func):
-            func = defer.Deferred().addCallback(func, *args, **kwargs)
-        assert isinstance(func, defer.Deferred), \
-            'prepend_callback expects a callable or defer.Deferred instance, got %s' % type(func)
-        self.deferred = chain_deferred(func, self.deferred)
-        return self.deferred
-
     def set_url(self, url):
         assert isinstance(url, basestring), \
             'Request url argument must be str or unicode, got %s:' % type(url).__name__