issue 1253 - prevent multiple logins with same username
fixed naming of strings and changed from i to I
Uses callback for players already in World.
removed GetUsernames() from World
removed extra space and fixed some formatting in cCallback
Changed Kick message
changed from using iterator to auto for server and clienthandle
Merge branch 'issue_1253' of https://github.com/p-mcgowan/MCServer into issue_1253
Moved the check into a new function and just calls that function and a blank FindAndDoWithPlayer added.
Changed HandleHandshake to return the result of CheckMultiLogin instead of just true since it already returns true if it finds and kicks the current player.
removed last space in handlehandshake
Fixed compile errors
created callback in Root and changed CheckMultiLogin() to use the DoWithPlayer function at Root instead of World.
Added NetherOreNests to nether default generator.

Now there's quartz in the nether
Changed CheckMultiLogin() to not have main body wrapped in an if statement.
Added in indent to cPlayerListCallBack in cCallback class inside CheckMultiLogin().
Added doxy-comment for DoWithPlayer().
Changed comments on IsPlayerInQueue() and IsAllowMultiLogin() to doxy-comments.
Changed DoWithPlayer to auto instead of using iterator.
Fixed indent problems and added return definitions to CheckMultiLogin().
Changed from IsAllowMultiLogin() to DoesAllowMultiLogin().
Fixed CheckMultiLogin() to not run to the end without returning a value.
Fixed return value in CheckMultiLogin()
Changed method call to DoesAllowMultiLogin() instead of IsAllowMultiLogin()
Compiles correctly.
Merge pull request #1623 from p-mcgowan/issue_1253

Prevent multiple logins with same username, unless allowed in settings