max_input_size around the wrong way -- it returns the output token
size for a given input size, rather than the maximum input size for a
given output token size.
From: Luke Howard <lukeh@PADL.COM>
git-svn-id: svn://svn.h5l.se/heimdal/trunk/heimdal@12352 ec53bebd-3082-4978-b11e-865c3cabbd6b