Bug in TColStd_PackedMapOfInteger regarding storage of negative values

When a negative key is put in TColStd_PackedMapOfInteger it is available in the
container by iteration, but there are several incorrect scenarios of behavior:

 - method Add with the same value always returns true, as if this key is being
put to the map for the first time, and the map extent incremented each time.
 - method Contains says there is no such key in the map.
 - method Remove does not remove such key from the map.
 - boolean methods work incorrectly as well.

The test program is attached here.