small doc update

doc/library/config.txt

@@ -573,12 +573,14 @@ import theano and print the config variable, as in:
 
   Default ``auto``
 
-  If ``auto``, auto detect if cudnn is there, if not, raise an error.
+  If ``auto``, auto detect if cudnn is there, if not, do not use it,
+  but do not raise an error.
 
   If ``True``, if we can't use cudnn, raise an error.
 
   If ``False``, do not test if cudnn is there and don't use it.
-  Useful to disable it completly when the auto detection crash in some strange case.
+  Useful to disable it completly when the auto detection crash in some
+  strange case.
 
 .. attribute:: config.dnn.conv.workmem
 

doc/library/sandbox/cuda/dnn.txt

@@ -38,7 +38,7 @@ By default, Theano will detect if it can use cuDNN. If so, it will use
 it.  If not, Theano optimizations will not introduce cuDNN ops. So
 Theano will still work if the user did not introduce them manually.
 
-The recently added Theano flag :attr:`allow_gc <config.dnn.enabled>`
+The recently added Theano flag :attr:`dnn.enabled <config.dnn.enabled>`
 allow to change the default behavior to force it or disable it. You
 can also get an error with older Theano version if cuDNN can not be
 used, by using this Theano flag: ``optimizer_including=cudnn``.