Document undocumented changes from Athena 9

[jdreed]

This ticket will collect a list of changes from Athena 9 that have not yet been documented, but should be.

[jdreed]

• we don't set athena_path anymore, except for tcsh users of .path
• we don't set athena_manpath (discussed might be changed for tcsh users)
• LD_LIBRARY_PATH is not set by default (because /usr/athena/lib is now a symlink)
• we no longer set noclobber in bash
• we don't set PS1 or CDPATH in bash

[jdreed]

zwgc does not run by default on dialups (See trac #137, may be changed to conditionalize on fallback=true as per zephyr discussion on 3/10)