Add sup expression
Add rake 10.0.4 expression, use new rake version in sup build
Compile libusb with gccApple on darwin
Add gpgme build input for sup
gnupg: fix building on darwin

* fix spelling error
* add libiconv to build inputs
Tidy up new rake version
sup: separate dependencies

create separate expressions for gems requiring native extensions to be
built:

* gpgme
* ncursesw_sup
* xapian_full_alaveteli