Per http://www.open-mpi.org/community/lists/devel/2008/04/3778.php, Ralph W.'s suggestion to remove an unnecessary escape

This commit was SVN r18354.

config/ompi_functions.m4

@@ -132,7 +132,7 @@ case "$prefix" in
     echo installing to directory \"$prefix\" 
     ;;
   *) 
-    AC_MSG_ERROR(prefix \"$prefix\" must be an absolute directory path) 
+    AC_MSG_ERROR(prefix "$prefix" must be an absolute directory path) 
     ;;
 esac