Clarifications on the first(), next(), and previous() functions, based

on comments from Detlef Lannert <lannert@lannert.rz.uni-duesseldorf.de>.

Doc/lib/libbsddb.tex

@@ -95,18 +95,19 @@ Set the cursor to the item indicated by the key and return it.
 
 \begin{methoddesc}{first}{}
 Set the cursor to the first item in the DB file and return it.  The order of 
-keys in the file is unspecified.
+keys in the file is unspecified, except in the case of B-Tree databases.
 \end{methoddesc}
 
 \begin{methoddesc}{next}{}
 Set the cursor to the next item in the DB file and return it.  The order of 
-keys in the file is unspecified.
+keys in the file is unspecified, except in the case of B-Tree databases.
 \end{methoddesc}
 
 \begin{methoddesc}{previous}{}
 Set the cursor to the first item in the DB file and return it.  The
-order of keys in the file is unspecified.  This is not supported on
-hashtable databases (those opened with \function{hashopen()}).
+order of keys in the file is unspecified, except in the case of B-Tree
+databases.  This is not supported on hashtable databases (those opened
+with \function{hashopen()}).
 \end{methoddesc}
 
 \begin{methoddesc}{last}{}