Add detail and clarifications to syncdb/migrate
Add Fabric commands drop_db and upgrade
Fabric update_db fixes

_migrate_fake for initial `migrate --fake 0001` for 2.5->2.5.1 conversion
(but only if it is still needed!)

Eliminate extra settings(hide(...)) unneeded for setup_db/update_db
Documentation cleanup for deploy README.rst
Add working version of update_staging script

Apart from being an example of copying one deployment to another, this also
provides an example of using Fabric commands for performing a Pootle upgrade.
Enable Firefox project setup for update_staging

Also create debug UI languages
Copy Pootle PODIRECTORY too

[ci skip]
Add workaround for Connection Refused exceptions

When performing a number of ssh commands in quick succession with Fabric
some sort of rate limiting is kicking in; causing following commands to
get Connection Refused errors.  Sticking a few sleeps here and there seems
to help.
Add warning about --fake
Generate pinned and minimum requirements

For testing and deployment purposes, it is very helpful to have pinned
requirements (that won't change when a new release comes out).  It is
also useful to be able to test the purported minimum versions that are
supported, to see if that is in fact true.

This commit does not set up that testing infrastructure, but does add
minimum versions to many requirements, and generates requirements.txt
and a new min-required.txt with minimum claimed supported versions.

This is part of the resolution for Bug 3005.
Generate HTTP Expires headers

Per Django tuning suggestions in bug 2935, this sets image expirations
to 2 hours, and (versioned) CSS/Javascript to 10 years.
Fix broken template formatting

$()s will not be substituted - only %()s
Improve error message

I am constantly setting PYTHONPATH=`pwd` but it has no effect - it needs
to be exported into the environment, make the error message reflect that.
Docs: improvements on upgrade docs