Lint .Call() of another package's routines

[MichaelChirico]

R CMD check enforces this:

.Call("routine", PACKAGE = "somebody.elses")

E.g.

* checking foreign function calls ... NOTE
Foreign function call to a different package:
  .Call("readProtoFiles_cpp", ..., PACKAGE = "RProtoBuf")
See chapter 'System and foreign language interfaces' in the 'Writing R Extensions' manual.

This is basically the same as restricting ::: -- if {lintr} is aware of the current package's name, we could enforce this during development to avoid waiting for R CMD check.