added specific capability_type, fix #78

[drzraf]

fix #78

[sque89]

hi @mikelittle, could this be merged soon?

[mikelittle]

We have to consider a change like this carefully as it will break functionality for any existing installs where, for instance, authors are allowed to create redirects. In the meantime, you could use the register_post_type_args filter to add the argument yourself