Bug fix to the EOF handling and also a simplification.

We incorrectly reported the lack of an EOF block when checking a
sub-range, where we get an expected EOF at the end of range but this
isn't due to a file EOF.

Simplifying this the API now uses scram_eof() returning 0 for false, 1
for expected eof and 2 for unexpected eof (no EOF block).


git-svn-id: svn://svn.code.sf.net/p/staden/code/io_lib@3549 ba6f2710-ca9f-427c-89d3-5bf716dbc8e1