Downgrade CaskAlreadyInstalledError to a warning

Automatic installs - like thoughtbot's laptop script - fail when we
use Homebrew's onoe method.  Using opoo (to warn) will let the
scripts complete successfully when they try to install packages that
have already been installed.

Test for downgrading AlreadyInstalledError to warning
update praat.rb to version 5.4.00

* update version/checksums
* re-use `version` value
* define `license`
Merge pull request #6968 from rolandwalker/update_praat

update praat.rb to version 5.4.00
fix checksums for older-OS Macports
Merge pull request #6969 from rolandwalker/macports_checksums

fix checksums for older-OS Macports
Merge pull request #6823 from ffleming/downgrade-error

Downgrade CaskAlreadyInstalledError to a warning