MySQL: point caveats to proper version
beecrypt: fix compiles on 64-bit systems

Closes #18889.
Make testing_env somewhat readable
formula_installer: warn on bottles being skipped.

We want to notify users that non-/usr/local installs may result in some
bottles being not used.

References #18540
Add optional post_install method to Formula.

Sometimes we may want to run commands after bottle installation (such as
creating directories outside the Cellar) so this method allows us to do
so.

Closes #18382.
mysql: fix creation of var/mysql when pouring.
Requirement: env DSL is evaluated in context of self, not ENV

This was meant to support:

  env do |req|
    append_path 'PATH', req.some_method
    ...
  end

i.e., the block was evaluated in the context of ENV. But it turned out
to be not so useful after all, so I'm ripping it out before something
actually depends on it.
Fix X11 env setup
Test that X11 env is triggered correctly
Remove broken aliases