hgweb: always start graph with the revision in url stable

hgweb: always start graph with the revision in url

It is the same fix for graph command, as was recently for log. This makes the
specified revision be always on top of the graph view.
Before the patch, for example with repo having revisions 0, 1, 2, 3 and revision
in url being '2', all revisions were shown and the specified one wasn't
the first.

--- a/mercurial/hgweb/webcommands.py	Thu Jul 25 00:44:00 2013 -0500
+++ b/mercurial/hgweb/webcommands.py	Thu Jul 25 02:48:21 2013 +0400
@@ -879,8 +879,7 @@
     count = len(web.repo)
     pos = rev
     start = max(0, pos - revcount + 1)
-    end = min(count, start + revcount)
-    pos = end - 1
+    end = pos + 1
 
     uprev = min(max(0, count - 1), rev + revcount)
     downrev = max(0, rev - revcount)

--- a/tests/test-hgweb-commands.t	Thu Jul 25 00:44:00 2013 -0500
+++ b/tests/test-hgweb-commands.t	Thu Jul 25 02:48:21 2013 +0400
@@ -1324,14 +1324,11 @@
 
   $ "$TESTDIR/get-with-headers.py" 127.0.0.1:$HGPORT \
   >   'graph/e06180cbfb0?style=raw&revcount=3' | grep changeset
-  changeset:   ab4f1438558b
   changeset:   e06180cbfb0c
   changeset:   b4e73ffab476
 
   $ "$TESTDIR/get-with-headers.py" 127.0.0.1:$HGPORT \
   >   'graph/b4e73ffab47?style=raw&revcount=3' | grep changeset
-  changeset:   ab4f1438558b
-  changeset:   e06180cbfb0c
   changeset:   b4e73ffab476
 
   $ cat errors.log