add missing change in BaseBuiltIn.html for fix of 'Repeat page title block in <head><title>...</title></head> and <body></body>'
merged with changes from upstream https://github.com/wickens/django-ptree.git
Fixed:  "Hide a session" (formerly, "Hide a sequence of experiments"): SessionParticipant objects (formerly "Participant in sequence of experiments") should be filtered as well.
"Categorize apps in the ModelAdmin": "Session" should be the first app on that page.
PTree Change List: fixed text clipping in cells, fit more text into the cells
Fixed a bug in 'Display app names without underscores'
"Categorize apps": If a section is empty, the header should be hidden too.
in the middle of some fixes to form choices
merged most recent changes from jacob
updated export format and refactored adminlib