Fixing two 1-line typos.

Fixing two 1-line typos.
latexdoc/generaldescription.tex

This was mentioned on the list a week or two ago.
Fix eliminates a duplicated word pair from the document.
-\addtoindex{mangled names}
-mangled names.
+\addtoindex{mangled names}.

Noticed this when looking at the index entries for mangled
names (we do not want the ! to appear in the body of text).
-\addtoindex{names!mangled}
+\addtoindexx{names!mangled}