Fixed one typo in response_helpers which caused is_admin context variable not to work correctly. Created new checkLinkNameForId function that checks if link_name is correct when creating new user and modifying existing one. This is now used for validation instead of doesLinkNameBelongToId in UserForm clean_link_name function. The previous validation function didn't allow to create new users and modify linkname of existing ones. Additionally I created new doesLinkNameExist helper function.

"""Multi-consumer multi-producer dispatching mechanism
"""
__version__ = "1.0.0"
__author__ = "Patrick K. O'Brien"
__license__ = "BSD-style, see license.txt for details"