AD support bug fixes

[whm]

This update includes the following changes.

• Resolves several problems that prevented creating of most keytabs using the AD backend.
• Correctly sets the userPrincipalName in AD so that the original principal names for service keytabs can be used in addition to the AD specific samAccountName. samAccountNames are restricted to 20 characters and must be unique. For principal names that exceed this length a samAccountName is unique samAccountName is formed by truncating the original principal name and appending an integer. This allows arbitrarily long principal names.
• The contributed script ad-keytab is installed by default. The script can be used to boot strap the AD backend and to examine the raw AD keytab entries.

[rra]

I think everything in this change was superseded by the changes I just merged from your ad-updates branch. If not, could you try to reconcile these changes with the current master branch and update this PR with the remaining changes? The two PRs conflicted, and the ad-updates branch seemed to be more complete, but I could well be misreading things.

[whm]

You are exactly correct. The ad-updates branch had my most current version of the AD support. Thanks for all of the work tidying up my spelling and code.

Bill