FIX: properly reset all contexts after forking

Fixes hang on backup

script/check_forking.rb

@@ -0,0 +1,28 @@
+require File.expand_path("../../config/environment", __FILE__)
+
+def pretty
+  puts "<before>"
+  puts PrettyText.cook("My pid is #{Process.pid}")
+end
+
+Discourse.after_fork
+pretty
+
+child = fork do
+  Discourse.after_fork
+  pretty
+  grand_child = fork do
+    Discourse.after_fork
+    pretty
+    puts "try to exit"
+    Process.kill "KILL", Process.pid
+  end
+  puts "before wait 2"
+  Process.wait grand_child
+  puts "after wait 2"
+  Process.kill "KILL", Process.pid
+end
+
+puts "before wait 1"
+Process.wait child
+puts "after wait 1"