--- a/enable.sh	Tue Mar 20 16:58:00 2012 +0100
+++ b/enable.sh	Tue Mar 20 17:04:05 2012 +0100
@@ -3,6 +3,11 @@
 here=`readlink -f "$0"`
 repo_root=`dirname "$here"`
 
+if !( hg --version -q | grep -e 'version 2\.[1-9]' ); then
+    echo 'You need mercurial 2.1 or later' >&2
+    exit 2
+fi
+
 
 
 cat << EOF >&2