[1.2.X] Fixed #7077 and #7431 -- Use getpass.getuser instead of pwd.getpwuid...

[1.2.X] Fixed #7077 and #7431 -- Use getpass.getuser instead of pwd.getpwuid to determine the current system user's username in the createsuperuser management command to enable the feature on Windows. getpass.getuser automatically falls back to the previous method.

Backport from trunk (r14607).

git-svn-id: http://code.djangoproject.com/svn/django/branches/releases/1.2.X@14608 bcc190cf-cafb-0310-a4f2-bffc1f526a37