Added basic doc for HA
Added singleton and voting sections and corrected

I addressed several redaction issues and added sections for
voting and singleton workers as commented by @rogpeppe
Made gramatical corrections suggested by @mjs
added dry run support for upgrade-juju
simplified upgradejuju dry run test
changed upgrade-juju dry run option to --dry-run
Re wrote backup in go

Previously restore was a cmd plugin writen in bash.
Backup was implemented as a go function, still not in use.
Tests where added since the previous implementation had none.
backup package includes:
 * BackUp function, which performs the actual back up.
 * tarFiles which creates a tar or tar.gz/tgz depending
on the output file name given.
 * runCommand which is a convenience function to simplify testing
since the back up process requires calling external executable
mongoexport.
Added note on singleton vs concurrent

After talking with @fwereade I added a note explaining that
singletons, as they are documented righ now, are only a reflection
of current status but should be considered as wrong and will be
re-implemented properly, as concurrent workers, in the future.
Corrected two gramatical errors
added test for call dispatching
made the test more standard conform
Merge branch 'master' of https://github.com/juju/juju into fix-api-params

# By Ian Booth
# Via Ian Booth (1) and Juju bot (1)
* 'master' of https://github.com/juju/juju:
  Tweak hpcloud boilerplate to turn floating-ip and remove az from example region
Refactored according to reviews

After reviews from @rogpeppe, @howbazaar, @mjs and @voidspace y
refactored a large part of how the tar files are tested, and
how the tar files are generated (most of that logic is to be
credited to @rogpeppe).
Now tar/tar.gz are built recursive and support prefixes to be
stripped if necessary (equivalent to -C on gnutar).
Tests check for files inside the tar and for the sum
Backup returns (filename, sum, err) instead of previous (filename,
sumfilename, err).
Introduce Parse{Unit,Service,Machine}
Merge branch 'master' of https://github.com/juju/juju into 106-parsetag-refactor

Conflicts:
	state/api/deployer/unit.go
	state/api/firewaller/service.go
	state/api/provisioner/machine.go
wip
Merge branch 'master' of https://github.com/juju/juju into fix-api-params
added log to intruct the user how to run this command to update to a particular version
made output prettier based on fwereade's feedback
Display welcome message when starting debug-hooks sessions.