Memory is accumulated as BUFR messages are processed

[sandorkertesz]

For the temp.bufr file (500KB, a few hundred messages) from the test samples if we run a simple extraction the peak memory usage is 1.5. GB! Simple tests show that the memory allocated to the message handle is not released after the message is processed in the main message loop.

[iainrussell]

This was a really good catch - well done Sandor!