[ooxml-branch] Split the common ss interfaces into two sets - one that works with...

[ooxml-branch] Split the common ss interfaces into two sets - one that works with jdk 1.5 and has the full functionality, and another that works with jdk 1.4 and only has dummy functionality. Update build.xml to spit out two versions of the main classes, one for jdk 1.5 with the full interfaces, and one for jdk 1.4 with the dummy ones (but which is otherwise like the current behaviour). Also add readme explaining all this

git-svn-id: https://svn.apache.org/repos/asf/poi/branches/ooxml@613951 13f79535-47bb-0310-9956-ffa450edef68