eliminates a raft of portability issues, including whether sys_nerr
exists, whether the platform has any valid negative errnos, etc.  The
downside is minimal: errno shouldn't ever contain an invalid value anyway,
and if it does, reasonably modern versions of strerror will not choke.
This rangecheck idea seemed good at the time, but it's clearly a net loss,
and I apologize to all concerned for having ever put it in.

optimized away completely.

included, and then include <strings.h> if so.  Several systems already
needed <strings.h> anyway.  Some new systems that claim to conform to the
Unix 9x "standard" do not declare str[n]casemp() in string.h, and C99
compilers will not like that.

Update the installation instructions (formerly misnamed "FAQ"), add configure
checks for some headers rather than having users copy stubs manually (ugh!).
Use Autoconf check for exe extension.  This also avoids inheriting the value
of $(X) from the environment.

Interfaced a lot of the custom tests to the config.cache, in the process
made them separate macros and grouped them out into files. Made naming
adjustments.

Removed a couple of useless/unused configure tests.

Disabled C++ by default. C++ is no more special than Perl, Python, and Tcl.
And it breaks equally often. :(