Improve BotAI.already_pending

[Dentosal]

• Count instances of this building already in progress
• Count workers currently moving to build the given building

[reypader]

I was able to rework BotAI.already_pending in the build-order-support branch to instead return the count and rely on falsy/truthy values. I'll cherry-pick it and create a PR.

[reypader]

It might be good to also include support for upgrade detection in already_pending.

[reypader]

PR #21 has been fixed to return 0 when none of the conditions are met

[Dentosal]

Merged.