[except] Fix index entry for 'exception object' (#1865)

Author: jensmaurer

source/exceptions.tex

@@ -5,7 +5,7 @@
 \gramSec[gram.except]{Exception handling}
 
 \indextext{exception object|see{exception handling, exception object}}%
-\indextext{object, exception|see{exception handling, exception object}}
+\indextext{object!exception|see{exception handling, exception object}}
 
 \pnum
 Exception handling provides a way of transferring control and information