Two last corrections:
- Viewport was not written during automatic export of XML files, because Virtualization of XMLSettingsTree did not work due to inconsistent function definition (const vs. non-const)
- Some of the default parameter-file had "Start saving movie frames" switched on by default, dramatically slowing down the example runs. Now it is switched off in all example XML files.

user: Roeland Merks <roeland.merks@cwi.nl>
branch 'default'
changed data/leaves/auxin_growth.xml
changed data/leaves/tutorial5_init.xml
changed src/VirtualLeaf.cpp
changed src/mainbase.cpp
changed src/mainbase.h