bootstrap.sh: allow overring the tag to checkout by setting the TAG environment variable (helpful for debugging)

replace '-t 0' test with an environment variable since '-t 0' is false when standard input has been redirected and doesn't tell us whether or not we can use dialog for input, but Vagrant must be non-interactive

Added dialogs, so that the setup.sh can ask the user any questions even when its piped; Added additional email valdidation for the last step

short_open_tag=Off was mistakenly left in the earlier merge (was a fix for my old autodiscover.php but not needed with z-push), also regrouping the nginx directive to be near the rest of Z-Push

z-push autodiscover should use the primary hostname for the mail server and not the domain part of the email address (both may work, but the primary hostname is more likely to have a signed SSL cert)

* zen.spamhaus.org
* dbl.spamhaus.org
* checks if a connection to Google's MTA on port 25 works

broken in 04454b35

fixes #143

closes #19

whats_next: when there are multiple responses like for NS records sort the responses so we can compare to a fixed order

Merges branch 'owncloud' of github.com:jkaberg/mailinabox
which is pull request #135, closes #135

thanks @jkaberg, @fmbiete, @owncloud

based on a script by @jkaberg in #141

owncloud will only let users access it from the PRIMARY_HOSTNAME (due to its trusted_domains option being set statically), so only include /cloud in the nginx configuration for PRIMARY_HOSTNAME