SYNOPSIS
string make_shared_string (string str)
DESCRIPTION
Puts <str> in _the_ list of shared strings of the game.
If the string is used by several variables/objects this
saves memory. Keys of alists and mappings are always shared
strings.
BUGS
A better string handling in the driver should make this
efun unnecessary.
HISTORY
Introduced in LDMud 3.2.6; following a suggestion from TubMud.