remove useless define and more verbose error message.

configure.in

@@ -39,9 +39,9 @@ AC_CACHE_CHECK(for db_create in -ldb, ac_cv_db_db_create,
 		[db_create();],[ac_cv_db_db_create=yes])])
 if test $ac_cv_db_db_create=yes; then
 	LIBS="$LIBS -ldb"
-	AC_DEFINE(HAVE_LIBDB, 1, [Define if you have libdb])
 else
-	AC_MSG_ERROR([Berkley DB not found, you must install libdb])
+	AC_MSG_ERROR([Berkley DB not found.
+You must install libdb including the respective development files/headers.])
 fi
 
 AC_OUTPUT(Makefile src/Makefile isync.spec)