#504564 - Make summary length behave with fields

#504564: Make summary length behave with fields changes the way 'trimmed' text fields are displayed, by introducing a 'trim_length' formatter setting for each field separately, instead of previously :
- for fields on nodes, trimming to the length specified in the 'teaser_length_[node_type]' variable global to the node type
- for fields on other entities, trimming to 600 chars, period.

Head2Head update:
For each instance of type 'text_long' or 'text_with_summary' on nodes :
For each view mode where the formatter is 'text_trimmed' or 'text_summary_or_trimmed' :
$instance['display'][$view_mode]['settings']['trim_length'] = variable_get('teaser_length_' . $node_type, 600);