Replace sregex with rx, remove local copies of sregex and tree-widget.

sregex is now obsolete and replaced by rx. tree-widget is now included
in Emacs. Closes https://sourceforge.net/p/jdee/bugs/29/

git-svn-id: svn+ssh://svn.code.sf.net/p/jdee/code/trunk@296 381a1f10-3442-0410-997e-ef331cd04102