Add dynamic_bin_dir method

[shawnlaffan]

[WIP]

As discussed in PerlAlien/Alien-curl#10 (comment)

Still to do:

• It needs tests, but I'm not entirely sure where they should go.
• The system case is identical to that for bin_dir. Should it be? Or is this likely to cause problems when system libs are statically compiled? (Although there is no control at this level over system libs being static or dynamic).

[plicease]

* [ ]  It needs tests, but I'm not entirely sure where they should go.

Tests should go in t/alien_base.t, ideally as a new subtest. May need to create a new mock alien in the corpus directory.

* [ ]  The system case is identical to that for bin_dir.  Should it be? Or is this likely to cause problems when system libs are statically compiled?  (Although there is no control at this level over system libs being static or dynamic).

I am undecided on this point tbh. I am also not sure if this method shouldn't be called dynamic_dir.

[shawnlaffan]

Thanks. Will look at the other tests in alien_base.t and adapt.

I'm also leaning towards dynamic_dir as the method name now you raise it.

In theory one could have an entire structure under there if it is set as the build target in the first place, so .../dynamic/bin, .../dynamic/include etc. That would have back-compat issues, though.

[shawnlaffan]

The two updates in a072676 and ce9723b change the method name to dynamic_dir and add tests. They also set the method to return the empty list when called on a system install - let me know if this needs to be changed.