adds cuke for work package type switching
keeps values when switching types
adds cuke for custom field behaviour on work package type switching
fixes custom_field_value permitance for params
refactors work package controller to always use work_package method
adapt specs
rewrote spec to improve readibility
use identical methods for ancestor/descendant fetching

Work packages use nested_set_now.
specs permissions for work_packages
enables finding projects by identifier, scoped by visible
updates changelog
Merge branch 'feature/rails3' into fix/type_switching

Conflicts:
	doc/CHANGELOG.md
Merge pull request #304 from opf/fix/type_switching