lib-linefilter: always strip attributes from line before comparing.

lib-linefilter: always strip attributes from line before comparing.

If the key is an attribute, tell the callback using ci->key=="attr"
rather than the magic of -num2 == -1, which can get set by other
doc:render-line functions.

When the key is a line from doc:render-line, properly strip all
attributes, both old and new style.

Signed-off-by: NeilBrown <neil@brown.name>