Fix automated rb-site installs with support-related defaults.

When running `rb-site install` in an automated mode (using --noinput),
things would fail if either --company or --admin-email were left out.
We were saving the default values of None, but the support data
generation couldn't serialize these to strings.

To get around this, some people tried posting empty strings (using "" or
'""').

We now normalize None or single/double quotes to an actual empty string.

Fixes bug #3544
Reviewed at https://reviews.reviewboard.org/r/6274/
Normalize authentication errors from SVN.

When failing to authenticate with a repository, the SVN backends will
return an error of "callback_get_login required." This looks like a bug
in Review Board, but is actually just an error message meaning that the
credentials were bad.

We now normalize these errors, converting them into an
authentication-related error. The SSL error handling code already did
this, but now all call sites use it.

Reviewed at https://reviews.reviewboard.org/r/6275/
Fix support redirect for local sites.

The "contact support" link wasn't expecting to get a 'local_site_name'
argument, and so it caused a 500 error. This change just makes it accept all
kwargs and ignore them.

Reviewed at https://reviews.reviewboard.org/r/6279/