templater: move specialized exception types to top

I'm going to add one more exception type.

mercurial/templater.py

@@ -30,6 +30,9 b' from . import ('
     util,
 )
 
+class TemplateNotFound(error.Abort):
+    pass
+
 # template parsing
 
 elements = {
@@ -1465,9 +1468,6 b' def _readmapfile(mapfile):'
     aliases.extend(conf['templatealias'].items())
     return cache, tmap, aliases
 
-class TemplateNotFound(error.Abort):
-    pass
-
 class templater(object):
 
     def __init__(self, filters=None, defaults=None, resources=None,