Some better message for tokenizing fails.

parso/python/normalizer.py

@@ -512,6 +512,9 @@ class ErrorFinder(Normalizer):
                 else:
                     message = 'unindent does not match any outer indentation level'
                 self._add_indentation_error(message, spacing)
+            else:
+                if leaf.value.startswith('\\'):
+                    message = 'unexpected character after line continuation character'
                 else:
                     match = re.match('\\w{,2}("{1,3}|\'{1,3})', leaf.value)
                     if match is None:

test/test_python_errors.py

@@ -111,6 +111,7 @@ FAILING_EXAMPLES = [
     r'"',
     r"'''",
     r"'",
+    r"\blub",
 
     # SyntaxErrors from Python/symtable.c
     'def f(x, x): pass',