User can change display name to existing one even if Site settings require unique display names

Had to redo the pull request which is now #179 because I did some other mistake using Git.

This is not fixed in Platform 7.4.0 build 299
I can still EDIT the Username after having set "Require Unique Display Names" to TRUE and saved the change

I changed more than 1 UserName AFTER saving the change to "Require Unique Display Names"

For each UserName I did change this error appears in the log.resources file:

[ERROR] DotNetNuke.Modules.Admin.Users.EditUser - System.Threading.ThreadAbortException: Thread was being aborted.
at System.Threading.Thread.AbortInternal()
at System.Threading.Thread.Abort(Object stateInfo)
at System.Web.HttpResponse.AbortCurrentThread()
at DotNetNuke.Modules.Admin.Users.EditUser.cmdUpdate_Click(Object sender, EventArgs e)

I've tested it on the latest build (7.4.1.243) - DisplayName can't be updated using already existing name when "Require Unique Display Names" is enabled.
Feature is working as expected.
However there is an exception that occurs during UserUpdateCompleted event.
This exception is thrown because Redirect is called with endResponse param set to True.
I've submitted a pull request to address thread abort exception.

Merged PR https://github.com/dnnsoftware/Dnn.Platform/pull/455

Verified fixed Platform 7.4.2 build 81 clean install & upgrade
See attachment