Changes in version 1.14:

'zupdate --recursive --destdir=dir' now keeps the file name component
following the last slash in directory arguments;
'../a'  recompresses the file ../a/b.gz to dir/a/b.lz, while
'../a/' recompresses the file ../a/b.gz to dir/b.lz.

The chapter 'Syntax of command-line arguments' has been added to the manual.
