Added underlining misspelled text while typing. It can be disabled by (F7) or the tools menu.
The underline is gone when the text object is deselected.
To install the patch, you will need to install the packages: aspell, libaspell-dev, aspell-en and libaspell15.
In order to include the new dependencies, the makefile has been changed, so you will need to run the following commands after applying it in order to recreate the makefile:
then of course
sudo make install and you have a xournal with speller support.