Re-apply rev 28529, applied from a wrong project (Zope trunk).

ZODB cache size is an integer (number of objects), not a number of bytes.

Because this change wasn't made in ZODB (the right project), it got
lost when I stitched in ZODB 3.3.1a1 yesterday.

lib/python/ZODB/component.xml

@@ -152,7 +152,7 @@
   <sectiontype name="zodb" datatype=".ZODBDatabase"
                implements="ZODB.database">
     <section type="ZODB.storage" name="*" attribute="storage"/>
-    <key name="cache-size" datatype="byte-size" default="5000"/>
+    <key name="cache-size" datatype="integer" default="5000"/>
     <key name="pool-size" datatype="integer" default="7"/>
     <key name="version-pool-size" datatype="integer" default="3"/>
     <key name="version-cache-size" datatype="integer" default="100"/>