cgiwrap_getenv wraps the getenv function for access to
environment variables, which are used to pass data to
CGI scripts. This version differs from the system
getenv in that it makes a copy of the value it returns,
which gets around problems when wrapping this routine in
garbage collected/reference counted languages by
moving the ownership of the data to the calling
function.
RETURN VALUE
v - a newly allocated copy of the value of that variable, or
NULL if not found.