A few last updates before submitting the revised Plant Phys. paper. Corrected the invocation of TransporterDialog and added parameter 'yield_threshold'

user: Roeland Merks <roeland.merks@cwi.nl>
branch 'default'
changed src/ChangeLog
changed src/VirtualLeafpar.tmpl
changed src/mesh.cpp
changed src/parameter.cpp
changed src/parameter.h
changed src/pardialog.cpp
changed src/pardialog.h
changed src/wallitem.cpp