problem with _checkouts deps for plugin dependencies with definition as package

[andrzejsliwa]

how to reproduce:

in project I made _checkouts with sym-linked external plugin repository:

|-- _checkouts
|   `-- rebar3_plugin -> ../../
|-- rebar.config
|-- rebar.lock
`-- src
    |-- example.app.src
    `-- example.erl

when I define plugins deps as package kind:

{plugins, [rebar3_plugin]}.

error is reported:

[master][~/example]$ rebar3 compile                                                                                             rvm:ruby-2.1.3
===> Missing registry entry for package rebar3_plugin
===> Plugin rebar3_plugin not available. It will not be used.
===> Verifying dependencies...

when plugin in deps is declared as git, everything is working:

{plugins, [{rebar3_plugin, {git, "", ""}}]}.

*[master][~/example]$ rebar3 compile                                                                                            
===> Compiling rebar3_plugin
===> Verifying dependencies...
===> Compiling example