Enhance test case for get_utf8.

I strengthened the test of the get_utf8 function by adding some UTF-8 chars to
the a2.fxl test, and making that test print each character on a separate line.
Before doing this, if you deliberately broke get_utf8 by making it return only
the first byte read, you would still see the correct test output because all
the individually read bytes stream together just fine.  Now if you break
get_utf8, you see a distinct difference in the test output.

Made cosmetic changes in test/a1.fxl and test/fib.fxl.