* environ.cc (parse_options): Use setenv to potentially replace CYGWIN value on

* environ.cc (parse_options): Use setenv to potentially replace CYGWIN value on
export.  Fixes broken behavior since November 2000 changes.
(regopt): Return indication of whether or not something has been parsed from
the registry.
(environ_init): Only attempt to export CYGWIN variable when values were set
from the registry.  It is exported automatically otherwise.