Parse common part of header and accept other years.

Parse common part of header and accept other years.

This patch allows files from other years to be transmited, but won't be
able to read all the data from the header, and won't be able to do extra
verification.

The only real verifications done is that the header size matches what is
expected for that year and there is a high level of confidence that the
head part of the header is really the same for the years supported by
rnetclient.

No other verification is done for the extra fields present in the file,
and all the extra data is not used any other place in the program
anyway.