Restore special case functionality of contains

The documentation for the contains method indicates that it should
return true if a single-value range matches the given value regardless
of the IncMin and IncMax parameters.  This commit restores this
behavior.
Add tests of contains method for bounding values

This commit adds 12 tests which check the behavior of the contains
method for bounding values as the IncMin and IncMax settings are
varied.
Correct contains method for max bound w/o IncMax

The comparison for an interval with only a maximum bound and
without the IncMax setting should be < rather than <=.