Properly implement protocol skipping in checker
Properly implement protocol skipping in checker

Network.HTTP can only check if http:// and https:// links resolve,
however there is much more scheme names than just `mail:`, `http://` and
`https://`.
They would be handed off to internal URI checker and would fail.

Javran/hakyll,beni55/hakyll,freizl/freizl.github.com-old,freizl/freizl.github.com-old,freizl/freizl.github.com-old,oldmanmike/hakyll,freizl/freizl.github.com-old,Minoru/hakyll,d12frosted/hakyll,freizl/freizl.github.com-old,freizl/freizl.github.com-old,freizl/freizl.github.com-old