Update validate_password()
Update validate_password()

validate_password()
- remove "and contain no illegal characters" misleading comment 
- rename parameters for a better understanding
- add is_string() check so null or bool values do not validate any more ( bug https://github.com/vexim/vexim2/issues/90 )
runout-at/vexim2,runout-at/vexim2,avleen/vexim2,avleen/vexim2,avleen/vexim2,runout-at/vexim2,Udera/vexim2,Udera/vexim2