This commit introduces a new OutputStream class for representing the
summary specification file (.SMSPEC). The stream is constructed
with constant data (output directory, basename, start date &c), and
provides a single write() member function that outputs a summary
specification.
Each call to write rewinds the underlying stream's output position.
Class EclOutput grants friendship to the new output stream class in
order to support easy stream rewinding.
Add a unit test to exercise the new class.
080225d8e5