Fixed Imakefile so that it compiles dlf in the dlf directory and common in the common directory (they were buidling each other in each other's directory????), and added the right depth (right number of ../) to the location of the dependent library directories.  Added RTCPDErrorMessage exception.

Marshaller code can now safely unmarshall strings.  Unlike the orginal C code, the new string unmarshaling code checks both the source and destination buffers.  The original C code did not check the source buffer and a server could crash on reception of a message containing a string with no terminator character.