Deprecate zero and one for Ptr{T}

They doesn't fulfill the documentation for zero and one about additive
and multiplicative identity.

See discussion in
https://github.com/JuliaLang/julia/pull/6183#issuecomment-61853347
Merge branch 'one_ptr' of github.com:ivarne/julia into ivarne-one_ptr

Conflicts:
	base/deprecated.jl
Merge branch 'ivarne-one_ptr'