Added flavors support to www/drush

[mfechner]

Summary

Commit message:
Added flavors support to drush.

I will refer to PR 227741.

Test Plan

Port build with poudriere and modified patch to make portlint happy.

[tz]

While the patch is fine, UPDATING needs an entry for it!

[mfechner]

There is already an entry existing (20180611).
If we start to add for each php application an entry that will cause the UPDATING file to explode or?

[tz]

In D15990#338873, @mfechner wrote:

There is already an entry existing (20180611).
If we start to add for each php application an entry that will cause the UPDATING file to explode or?

Nope. Also this entry is for the past. There are even more, like for 20180518 or 20180412.

The problem with not doing it because of 20180611 is: when using pkg updating with an date after 20180611 you wont notice it. And you need to fix the problem by yourself. So its better to have a short notice. You can even reference 20180611 if you want. But do not surprise the user with an unexpected problem ;)

[mfechner]

Added entry in UPDATING.

[tz]

Thanks swills! :)