interp: use strings to avoid buffer hell

I ended up here because clang warned about 'strncat(cmd, buf, sizeof(buf))'
-- strncat is notoriously difficult to use.  This usage is wrong, and
related code must be prepared to deal with a non-NULL-terminated character
array (which related code was not).

Use C++ strings instead, until it becomes inconvenient to (the place
where the string needs to be split at newlines)

Signed-off-by: Jeff Epler <jepler@unpythonic.net>
hal: an "increased" pin for thread time

.. this way you can trigger on "tmax-increased" when scoping for
overruns

Signed-off-by: Jeff Epler <jepler@unpythonic.net>
rtapi: remove support for rtlinux 3.x

No one answered the call for maintainers.  In fact, there's no sign that
rtlinux even exists for modern linux versions.

Signed-off-by: Jeff Epler <jepler@unpythonic.net>
rtapi: drop support for rtai "24.x"

.. this version of rtai was for kernel 2.4.x, which are no longer
supported.

Signed-off-by: Jeff Epler <jepler@unpythonic.net>
rtapi: drop support for alternate math libs

ever since we hardcoded the loading of rtai_math years ago, we have
never exercised the code path where we allow the use of diet or glibc
math libraries in kernel space.  Drop the related code.

Signed-off-by: Jeff Epler <jepler@unpythonic.net>
configure: drop never-used RTAI3_MOD variable

this may once have been used to dynamically list the rtai modules to be
loaded, but this list has been static for a long time.

Signed-off-by: Jeff Epler <jepler@unpythonic.net>
uspace: don't let ctrl-z stop realtime

.. if the rtapi_app process is the head of its own process group,
it is not subject to being stopped by ctrl-z in the terminal where it
was started.

Signed-off-by: Jeff Epler <jepler@unpythonic.net>
configure: don't require linux/version.h

This has been a legacy/unsupported header file for a long time, and
according to memleak is finally gone in kernels somewhere in the 3.x
days.  We have long looked at several alternative filenames to actually
find the magic constants, but for some reason required that the
version.h header exist at a certain spot even though we didn't use it
except as a last resort.

Signed-off-by: Jeff Epler <jepler@unpythonic.net>
Merge commit 'deb7aa4'

Signed-off-by: Jeff Epler <jepler@unpythonic.net>