... containing objects with no white-space between them.
To enforce the rule that objects end at the start-offset of the next
object, each object is parsed in it own object stream.
To facilitate this, a new private API input source is::OffsetBuffer has
been added which only contains the object but reports offsets relative to
the start of the object stream. This is adapted from OffsetInputSource by
changing the direction of the offset, endowing it with its own
BufferInputSource and striooing out checks duplicated in BufferInputSource.
Fixes the expected failure in the test case added in #1266.
