libhdfs++: hdfsRead return -1 at eof

The libhdfs++ implementation of hdfsRead appears to be out-of-spec. The header says it will return 0 at eof, but the current implementation returns -1 with an errno of 261 (invalid offset).

The basic posix-y read loop of
while ( (bytesRead = hdsfRead(...)) != 0)

won't work with with libhdfs++'s hdfsRead method.