Changing behaviours breaks recompilation

[filmor]

The Erlang compiler apparently always uses the loaded Mod:behaviour_info/1 to check whether a module implements the given behaviour. If it is changed, compiled modules will still be checked against the previous version of the behaviour and the compilation will either fail or (worse) go through even though the modules don't actually implement the new behaviour.

It's probably enough to forcibly unload modules that have a behaviour_info and are to be recompiled.

[vans163]

rebar_agent:do(compile) is used, if this happens this is a problem with rebar itself.

[filmor]

The problem doesn't happen with r3:do(compile). on a rebar shell, though.

[vans163]

Give this a new try please, I have released v0.5.1 which uses r3:do(compile) instead of rebar3_agent:do(compile)