Ensure we wrap the decorated functions

To avoid losing the original functions docs, name
and other attributes ensure that this correctly uses
six.wraps (which uses functools.wraps internally) to
wrap the decorated function.

retrying.py

@@ -55,6 +55,8 @@ def retry(*dargs, **dkw):
     # support both @retry and @retry() as valid syntax
     if len(dargs) == 1 and callable(dargs[0]):
         def wrap_simple(f):
+
+            @six.wraps(f)
             def wrapped_f(*args, **kw):
                 return Retrying().call(f, *args, **kw)
 
@@ -64,6 +66,8 @@ def retry(*dargs, **dkw):
 
     else:
         def wrap(f):
+
+            @six.wraps(f)
             def wrapped_f(*args, **kw):
                 return Retrying(*dargs, **dkw).call(f, *args, **kw)