[CMake] LIST command behavior changes

[Andy Cedilnik]

Hello,

After comments received from several people on the list, I modified LIST 
command. This breaks the behavior from the CMake beta's, so make sure to 
modify your code once Bill releases 2.4.2.

A side comment, since LIST command was not in any release yet, this 
should only affect people on the cutting edge.

So, the behavior changed in the following ways:

* LIST(SET  is gone
* LIST(APPEND now works even if the list does not exists yet
* LIST(GET will return NOTFOUND if the list does not exists but it will 
still complain about being out of range
* LIST(INSERT now works even if the list does not exists as long as the 
index is 0
* LIST(REMOVE is gone
* LIST(REMOVE_AT is now the one that removes index
* LIST(REMOVE_ITEM removes specified items and also removes specified 
item multiple times

More list commands will be added in 2.6.

-- 
Andy Cedilnik
Kitware Inc.