Add support for whitespace control in ftdetect

[SegFaultAX]

Docs: http://jinja.pocoo.org/docs/templates/#whitespace-control

Whitespace can be controlled before and after jinja tags by adding a - to the appropriate jinja block marker.

{% for i in [1,2,3] %}
  # ... SNIP ...
{% endfor %}

becomes

{% for i in [1,2,3] -%}
  # ... SNIP ...
{%- endfor %}

[Glench]

Thanks!