Added a check to XMLParser so that any element that uses idref cannot have other attributes or content. This should reveal XML errors where a reference was used but not indended so the content was ignored.
Added a check to XMLParser so that any element that uses idref cannot have other attributes or content. This should reveal XML errors where a reference was used but not indended so the content was ignored.

git-svn-id: 67bc77c75b8364e4e9cdff0eb6560f5818674cd8@1418 ca793f91-a31e-0410-b540-2769d408b6a1

svn2github/beast-mcmc,armanbilge/BEAST_sandbox,svn2github/beast-mcmc,armanbilge/BEAST_sandbox,svn2github/beast-mcmc,armanbilge/BEAST_sandbox,svn2github/beast-mcmc,armanbilge/BEAST_sandbox,armanbilge/BEAST_sandbox,svn2github/beast-mcmc