ACTION: EricP to extend < and relational ops to string, get review by Andy

I've updated the sorting order section to reflect that < is
responsible for all literals:
[[ http://www.w3.org/2001/sw/DataAccess/rq23/#defn_Ordered
RDF Literals are compared with the "<" operator (see the Operator
Mapping Table).
...
   1.  (Lowest) no value assigned to the variable or expression in
   this solution.
   2. Blank nodes
   3. IRIs
   4. RDF literals
]]

clarified the selection of operator definitions:
[[
When selecting the operator definition for a given set of parameters,
the definition with the most specific parameters applies. For
instance, when evaluating xs:integer = xs:signedInt, the definition
for = with two numeric parameters applies, rather than the one with
two RDF terms. The table is arranged so that upper-most viable
candiate is the most specific.
]]

Added four Operator Table Entries like:
  A < B		literal	literal	sop:literal-less-than(A, B)	xsd:boolean

Created sections for sop:literal-{less,greater}-than:
[[
11.2.3.0 sop:literal-less-than

Returns TRUE if the first argument sorts earlier than the second
argument according to this earliest rule in the sorting rules:

   1. Numerics sort before xs:dateTimes.
   2. xs:dateTimes sort before typed literals that are neither numeric
   nor an xs:dateTime.
   3. The remaining datatypes are compared with fn:compare. If the
   result is -1, the first argument sorts before the second
   argument. If the result is 1, the second argument sorts before the
   first argument. If the result is 0, the order is determined by the
   order of the lexical value of the datatypes. If fn:compare returns
   -1, the first argument sorts before the second argument. If it
   returns 1, the second argument sorts before the first argument. If
   it returns 0, the two arguments are equivelent.

11.2.3.0.5 sop:literal-greater-than

Returns FALSE if the first argument sorts earlier than the second
argument according to this earliest rule in the above sorting rules.
]]

and simplified sop:RDFterm-equal
[[
Returns TRUE if the two arguments are the same RDF term.
]]

I submit this to Andy's (and anyone else's) review.
-- 
-eric

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