Suppressed error message from `unalias which`

On debian (and possibly other) systems where which has no extended
options the preventive 'unalias which' produces error message. Redirected
to /dev/null.

Documentation edits

Really, REALLY last optimalization... I promise

- removal in comments
- _defwt renamed to _setwt
- change conditional in 'cle time'
- some output messages altered to be more clear

MayDay release of CLE

This should be final version for this month.
Hopefully all bugs were fixed, documentation edited to reflect current
fuctionality. New features will appear in next release.

This is "Spring" release of CLE

first named release... :-)

Easter release of CLE