[UNDERTOW-35] Enable Digest authentication for servlets.

[darranl]

Additional work is still needed within WildFly to enable this but no code changes should be required for WildFly to switch to a version of Undertow containing this change.

[undertow-pull-request]

Build 295 is now running using a merge of cba8251 on branch pull/87:
CI: http://teamcity.cafe-babe.org/viewLog.html?buildId=5159&buildTypeId=bt35
Extra info: Repository sources transferred: 67.11Kb total

[undertow-pull-request]

Build 295 outcome was SUCCESS using a merge of cba8251 on branch pull/87:
CI: http://teamcity.cafe-babe.org/viewLog.html?buildId=5159&buildTypeId=bt35
Extra info: Tests passed: 283, ignored: 8

[stuartwdouglas]

merged

[undertow-pull-request]

Build 297 is now running using a merge of cba8251 on branch pull/87:
CI: http://teamcity.cafe-babe.org/viewLog.html?buildId=5161&buildTypeId=bt35
Extra info: Running

[undertow-pull-request]

Build 297 outcome was SUCCESS using a merge of cba8251 on branch pull/87:
CI: http://teamcity.cafe-babe.org/viewLog.html?buildId=5161&buildTypeId=bt35
Extra info: Tests passed: 283, ignored: 8