Refactor: Remove support for multiple protocols

This removes the boilerplate code supporting more than one RPC protocol as it
was becoming hard to maintain and we probably won't ever need it.
Merge branch 'remove-multiple-protocol-support'
vim-patch:7.4.267

Problem:    The '[ mark is in the wrong position after "gq". (Ingo Karkat)
Solution:   Add the setmark argument to do_join(). (Christian Brabandt)

https://code.google.com/p/vim/source/detail?r=75f222d67cea335efbe0274de6340dba174c1e7e
Merge #756 'vim-patch:7.4.267'