Range Analyzer should tell whether range is looser than the source condition

(filed based on discussions with Igor)
Cost estimation code makes use of range analyzer to match (parts of) the WHERE
condition against column's Histogram.

Some other module (todo: which? MDEV#?) needs to know whether the estimate is
precise or not.

The main source of imprecision is that some of conditions are not [fully]
sargable. That is, range analyzer produces ranges that are wider than the
supplied conditions.

Examples of conditions with imprecise estimates:

  t.col < 10 AND t.col MOD 3 = 2 

  t.col LIKE 'foo%bar%'

Examples of conditions with precise estimates:

  t.col LIKE 'foo%'

  t.col < 3214

  t.col = 'bar'

  t.col IN (1,2,3) OR t.col BETWEEN 10 AND 20

(TODO: we don't need to handle the case of multi-column range analysis, do we?)