avoid $status and $options in POSIX mode

[Eric Blake <eblake@xxxxxxxxxx>]

POSIX states "The name space of environment variable names containing 
lowercase letters is reserved for applications. Applications can define 
any environment variables with names from this name space without 
modifying the behavior of the standard utilities."
http://www.opengroup.org/onlinepubs/9699919799/basedefs/V1_chap08.html#tag_08

Yet, the existence of zsh-magic variables like $status and $options 
infringe upon the right of a user's script to use this namespace for 
their own desires.  For example, see this recent autoconf patch:
http://git.sv.gnu.org/cgit/autoconf.git/commit/?id=23a2c336

It would be really nice if 'emulate sh' could disable zsh magic handling 
of any variables that infringe upon the lower-case namespace reserved 
for applications.

--
Eric Blake   eblake@xxxxxxxxxx    +1-801-349-2682
Libvirt virtualization library http://libvirt.org