Using `@service` replaces top-level module

[omus]

I expected that this would create a submodule within the user defined SQS module and not replace/merge with it:

julia> module SQS
       using AWS: @service
       const FOO = true
       @service SQS
       end
WARNING: replacing module SQS.
Main.SQS

This may also be motivation for allowing @service to support user-defined aliases

[omus]

Related to: #690

[omus]

Can be worked around with this:

julia> module _SQS
       using AWS: @service
       const FOO = true
       @service SQS
       end
Main._SQS

julia> const SQS = _SQS
Main._SQS

[omus]

The issue here is from Julia itself:

julia> module A
       end
Main.A

julia> A === A.A
true

julia> module B
       module B
       end
       end
WARNING: replacing module B.
Main.B

julia> B === B.B
false