Fixes #6117 - clean usergroup cache

Dependent destroy was missing on through association from user side.

Fixes #5941 - Handle nil comparison object in DHCP::Record.valid?

fixes #5826 - Using dots in kickstart template names or hostgroups causes routing errors

fixes #5834 - Hosts: . in the name is invalid - user is told this but the UI adds one anyway

fixes #5869 - permit accents in user names on Ruby 1.8

fixes #5671 - LookupValue name should be matcher, value is too long

fixes #5690 - determine host taxonomy fact based on setting value

Fixes #5664 - Host filters can use taxonomies

Also disables taxonomy filters on resources that do not support them.

Fixes #5637 - Don't raise lease conflicts when reading ad-hoc DHCP leases

fixes #5553: FiltersHelper#search_path returns an empty string for unrecognized resources