input/csv: unassorted adjustment, mostly "column processing" related

input/csv: unassorted adjustment, mostly "column processing" related

Reduce "state" in the CSV input module's context. Stick with variables
that are local to routines when knowledge of details need not be global.
Really base the processing of a column's input text on the column's
processing information which was gathered in the setup phase.

Rename few identifiers, to explicitly refer to logic channels (the only
currently supported data type of the CSV input module). Cease feeding
logic data to the session bus when there are no logic channels at all
(currently not really an option). Prepare for simpler dispatching of
parse routines should more data types get added in a future version.

Reduce some "clutter" (overly fragmented stuff that should go together
since it forms logical groups and is not really standalone). Address a
few more minor style nits (sizeof() redundancy, "seemingly inverse"
string comparison phrases).