Change ctc.root configuration variable from ConfigParam to StrParam

theano/configdefaults.py

@@ -1775,11 +1775,7 @@ AddConfigVar(
     'Directory which contains the root of Baidu CTC library. It is assumed \
     that the compiled library is inside the build directory, and the header \
     inside the include directory.',
-    ConfigParam(
-        '',
-        filter=filter_base_compiledir,
-        allow_override=False
-    ), in_c_key=False )
+    StrParam('', allow_override=False))
 
 # Check if there are remaining flags provided by the user through THEANO_FLAGS.
 for key in THEANO_FLAGS_DICT.keys():