Function: defvaralias

Make NEW-ALIAS a variable alias for symbol BASE-VARIABLE.
Aliased variables always have the same value; setting one sets the other.
Third arg DOCSTRING, if non-nil, is documentation for NEW-ALIAS. If it is
omitted or nil, NEW-ALIAS gets the documentation string of BASE-VARIABLE,
or of the variable at the end of the chain of aliases, if BASE-VARIABLE is
itself an alias. If NEW-ALIAS is bound, and BASE-VARIABLE is not,
then the value of BASE-VARIABLE is set to that of NEW-ALIAS.
The return value is BASE-VARIABLE.