Minor updates
Merge branch 'master' of github.com:maths/moodle-qtype_stack
Explicit output on the STACK libraries used.
Better ordering of error messages.
Fix the add node button on the editing form. Issue #65
Importing from older versions of STACK gives an error.
Merge branch 'master' of github.com:maths/moodle-qtype_stack
Merge branch 'master' of github.com:maths/moodle-qtype_stack

Conflicts:
	lang/en/qtype_stack.php
merge of land-file