update to subroutine UFBSEQ, including new test case

[jbathegit]

In my BUFRLIB repository in VLab, I have an update to subroutine UFBSEQ that I'd been planning to introduce in the next version for the WCOSS and on my website. Now that I'm working to fully merge everything into the NCEPLIBS-bufr repository on GitHub, I'd like to bring this update over to GitHub and just work from there going forward.

The update to the subroutine deals with a situation where the number of available data levels exceeds the amount of user-provided array space when reading from an input file. Previously, the software would abort in such cases without returning any data whatsoever, but with the change it will now print a diagnostic and return with the number of levels equal to the amount of array space that was provided. I have a sample test case for this situation and will include it as part of a new test program once I submit a pull request for this issue.