#30 Support for negative numbers in (T)SWITCH

[Wim Nelis]

This patch adds support for negative numbers in the (T)SWITCH transforms. The negative numbers were not allowed by the syntax check (module dm_templates.pm, function read_transforms_file), but were already allowed by the logic of the (T)SWITCH transform (module dm_templates.pm, function post_template_load). An inconsistency is removed: even if no comparison operator is specified, a non-integer number is allowed.