'forcerender' option to render dict now works. Updated docs.

docs/config.rst

@@ -387,6 +387,19 @@ values. The valid configuration keys are listed below.
         not get deleted. The only fix for this currently is to delete that
         render directory and render it again with :option:`--forcerender`. 
 
+``forcerender``
+    This is a boolean. If set to ``True`` (or any non-false value) then this
+    render will unconditionally re-render every tile regardless of whether it
+    actually needs updating or not.
+
+    The :option:`--forcerender`` command line option acts similarly, but giving
+    that option sets forcerender mode on *ever* render. With this option in the
+    config file, you can set a forcerender on just one of the renders.
+
+    You probably don't want to leave this option in your config file, it is
+    intended to be used temporarily, such as after a setting change, to
+    re-render the entire map with new settings.
+
 .. _customrendermodes:
 
 Custom Rendermodes and Rendermode Primitives

overviewer.py

@@ -299,6 +299,8 @@ dir but you forgot to put quotes around the directory, since it contains spaces.
         logging.error("You must specify at least one render in your config file. See the docs if you're having trouble")
         return 1
 
+    #####################
+    # Do a few last minute things to each render dictionary here
     for rname, render in config['renders'].iteritems():
         # Convert render['world'] to the world path, and store the original
         # in render['worldname_orig']
@@ -311,6 +313,10 @@ dir but you forgot to put quotes around the directory, since it contains spaces.
         render['worldname_orig'] = render['world']
         render['world'] = worldpath
 
+        # If 'forcerender' is set, change renderchecks to 2
+        if render.get('forcerender', False):
+            render['renderchecks'] = 2
+
     destdir = config['outputdir']
     if not destdir:
         logging.error("You must specify the output directory in your config file.")