facet_in_params should not call facet_field_in_params

blacklight_advanced_search needs to override facet_field_in_params?,
so it looks in params[:f_inclusive], not just params[:f]. But once
it does this, it breaks the previous facet_in_params, since it
assumed that if facet_field_in_params?, then params[:f][field]
must neccesarily exist. But we redefined it otherwise.

facet_in_params already needed to know about the internal details
of params structure, it already needed to look in params[:f][field]
itself -- now it just takes it's own responsiblity for making sure
params[:f][field] already exists before trying to look at it, instead
of assuming it knows the implementation of facet_field_in_params.

Getting blacklight_advanced_search to work without this patch is
going to take some hacks, so if a point release is possible it would
be helpful. But otherwise, can hack.
Merge pull request #790 from projectblacklight/independent_facet_field_in_params

facet_in_params should not call facet_field_in_params