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.

#!/bin/sh
NOSE_WITH_DOCTEST=t
export NOSE_WITH_DOCTEST
NOSE_DOCTEST_EXTENSION=txt
export NOSE_DOCTEST_EXTENSION
#NOSE_DETAILED_ERRORS=t
#export NOSE_DETAILED_ERRORS
nosetests $*