finish bloom filters

Add tuning, docs, etc.

Not sure if status is the right place to remote size.. perhaps unused
should report the size and also warn if it sees more keys than the bloom
filter allows?

debian/changelog

@@ -7,6 +7,14 @@ git-annex (3.20120310) UNRELEASED; urgency=low
     space, but now only needs to store the set of file contents that
     are present in the annex in memory.
   * status: Fixed to run in constant space.
+  * unused: Now uses a bloom filter, and runs in constant space.
+    Use of a bloom filter does mean it will not notice a small
+    number of unused keys. For repos with up to half a million keys,
+    it will miss one key in 1000.
+  * Added annex.bloomcapacity and annex.bloomaccuracy, which can be
+    adjusted as desired to tune the bloom filter.
+  * status: Display about of memory used by bloom filter, and
+    detect then it's too small for the number of keys in a repository.
 
  -- Joey Hess <joeyh@debian.org>  Sat, 10 Mar 2012 14:03:22 -0400
 

debian/control

@@ -18,6 +18,7 @@ Build-Depends:
 	libghc-lifted-base-dev,
 	libghc-json-dev,
 	libghc-ifelse-dev,
+	libghc-bloomfilter-dev,
 	ikiwiki,
 	perlmagick,
 	git,