MINOR: map/acl: add the possibility to specify the version in "clear map/acl"

This will ease maintenance of versionned maps by allowing to clear old or
failed updates instead of the current version. Nothing was done to allow
clearing everyhing, though if there was a need for this, implementing "@all"
or something equivalent wouldn't require more than 3 lines of code.
diff --git a/doc/management.txt b/doc/management.txt
index c15e71a..6ccd468 100644
--- a/doc/management.txt
+++ b/doc/management.txt
@@ -1495,15 +1495,19 @@
   server. This has the same effect as restarting. This command is restricted
   and can only be issued on sockets configured for level "admin".
 
-clear acl <acl>
+clear acl [@<ver>] <acl>
   Remove all entries from the acl <acl>. <acl> is the #<id> or the <file>
   returned by "show acl". Note that if the reference <acl> is a file and is
-  shared with a map, this map will be also cleared.
+  shared with a map, this map will be also cleared. By default only the current
+  version of the ACL is cleared (the one being matched against). However it is
+  possible to specify another version using '@' followed by this version.
 
-clear map <map>
+clear map [@<ver>] <map>
   Remove all entries from the map <map>. <map> is the #<id> or the <file>
   returned by "show map". Note that if the reference <map> is a file and is
-  shared with a acl, this acl will be also cleared.
+  shared with a acl, this acl will be also cleared. By default only the current
+  version of the map is cleared (the one being matched against). However it is
+  possible to specify another version using '@' followed by this version.
 
 clear table <table> [ data.<type> <operator> <value> ] | [ key <key> ]
   Remove entries from the stick-table <table>.