Check_MK Werk 8675: Fixed filtering on custom_variable_values columns.

ID: 8675 Title: Fixed filtering on custom_variable_values columns. Component: The Check_MK Micro Core Level: 1 Class: Bug Fix Version: 1.4.0i4 Previously even internal key/value pairs were considered when filtering on custom_variable_values, which is wrong and inconsistent with other operations on custom variable columns. This has been fixed.