Add a syntax for injecting args, to complement the new shepherd syntax

Hello @skuwamoto, 

Please review the following commits I made in branch 'nick-injectors'.

30566b213a229f021affc7146857d24519016be8 (2013-09-12 19:27:43 -0400)
Add a syntax for injecting args, to complement the new shepherd syntax


R=@skuwamoto