This module adds the "nameref" builtin command and implements most of
the predefined parameters in the "sh" namespace, for example
${.sh.lineno} and ${.sh.version}.  The previous patch to implement
PM_SPECIAL named references is required.

Where possible, these parameters are named references to the
corresponding zsh parameters, so ${.sh.version} is another name for
${ZSH_PATCHLEVEL}, etc.  Many of the remaining parameters are enabled
only in ksh emulation (as described in the documentation for the
module), to avoid function wrapper overhead in native mode.

I've included a documentation section describing some related features
that are NOT implemented, such as parameter discipline functions.  The
${.sh.name} and ${.sh.value} parameters are instead supplied for use
in user-defined widgets when "vared" is invoked.

There's a small change to utils.c to explicitly allow namespace
parameter syntax in ksh emulation mode.  We should perhaps reconsider
whether POSIX_IDENTIFIERS is really appropriate to be on by default in
ksh mode.