Fix loading random forests from an hdf5 file into an existing object.

If rf_import_hdf5() was called with an already populated random forest
object, trees and classes were appended to the existing data.
Add support for loading random forests from hdf5 files given by their id.
Fixed out-of-range exception of 1-dimensional VigraArrays (fixes #174)
finished tutorial page on Python bindings
Merge branch 'rf_hdf5' of https://github.com/burcin/vigra
fixed HDF5File and RandomForest constructor overloading (bug entered in 982ef6eabe9197938ff313d60fd47be8efe917a6)
use "<=" comparison instead of "<" in binary multi-morphology
cmake: increase template depth if necessary
Merge pull request #3 from ukoethe/master

from master to my branch