FOP-1801: conversion B&W GIF=>PDF creates PDF with colorspace RGB if FOP0.95 and Gray if FOP0.20.5; patch submitted by Thanasis Giannimaras following suggestion by Jeremias Maerki

git-svn-id: https://svn.apache.org/repos/asf/xmlgraphics/fop/trunk@1559284 13f79535-47bb-0310-9956-ffa450edef68