hg: jdk9/sandbox: Add support for finding pandoc.

[magnus.ihse.bursie at oracle.com]

Changeset: 5c94e415cc0c
Author:    ihse
Date:      2017-03-07 15:20 +0100
URL:       http://hg.openjdk.java.net/jdk9/sandbox/rev/5c94e415cc0c

Add support for finding pandoc.

! common/autoconf/basics.m4
! common/autoconf/generated-configure.sh
! common/autoconf/spec.gmk.in