clone: update to @ bookmark if it exists

mercurial/hg.py

@@ -409,7 +409,7 b' def clone(ui, peeropts, source, dest=Non'
             if update:
                 if update is not True:
                     checkout = srcpeer.lookup(update)
-                for test in (checkout, 'default', 'tip'):
+                for test in (checkout, '@', 'default', 'tip'):
                     if test is None:
                         continue
                     try:

tests/test-clone.t

@@ -468,6 +468,16 b' iterable in addbranchrevs()'
   $ rm -r ua
 
 
+Test clone with special '@' bookmark:
+  $ cd a
+  $ hg bookmark -r a7949464abda @  # branch point of stable from default
+  $ hg clone . ../i
+  updating to branch default
+  2 files updated, 0 files merged, 0 files removed, 0 files unresolved
+  $ hg id -i ../i
+  a7949464abda
+
+
 Testing failures:
 
   $ mkdir fail