deb: provide build-arch and build-indep targets

This is required by Debian Policy Manual section 4.9:

    https://www.debian.org/doc/debian-policy/ch-source.html#s-debianrules
These are needed for building and running on all platforms

(cherry picked from commit 3b03cefb49d964adaa9a83dc0f1775c4fdb97770)

Conflicts:
	debian/control.in
Fail on missing programs, instead of generating bogus scripts

(cherry picked from commit 0b5fba46aba7b35c8c3bcb80de43dec0ba8e97da)
Explicitly give the right build dependency for insmod/rmmod/etc

(cherry picked from commit 39e36ebd8fa5530ba87e162c17bac2c5ce57621f)

Conflicts:

	debian/configure
	debian/control.in
Merge remote-tracking branch 'origin/v2.5_branch' into 2.6

Conflicts:
	debian/configure (keep the 2.6 version)
	debian/control.in (keep the 2.6 version)
Merge remote-tracking branch 'origin/2.6'
src/configure: remove --enable-run-in-place

It's been deprecated since at least 2.4.0, time to remove it.  Configure
without providing a --prefix instead.
src/configure: use AS_HELP_STRING() everywhere

This makes the line-wrapping of the --help output automatic.

There are also some minor cosmetic changes to the help text: adding
missing punctuation and capitalization.
src/configure: --enable-simulator deprecation warning

Warn in the --help output that --enable-simulator is deprecated.
deb: remove unused variable in debian/rules

python_version is never used, it's just old cruft.
deb: debian/rules doesn't need to care about BUILD_SYS

The -X argument to dh_fixperms says to eXclude linuxcnc_module_helper
when it's fixing the permissions on all our files.  But dh_fixperm won't
complain or fail if it doesn't find linuxcnc_module_helper, so we don't
need to do this substitution trick to tell it what to expect.
deb: dont .gitignore package-dirs we no longer build
deb: get rid of ancient Provides in control

I think it's time to stop worrying about users upgrading from emc2.deb
packages.
deb: stop referring to the old "emc2" packages

They're long gone, no need to have them clog up our metadata any more.
uspace: make libudev optional

.. it's not available on debian kfreebsd.

Userspace PCI uses libudev to enumerate available PCI devices, and then memory
maps files in /sys to access the device.  Neither libudev nor this /sys interface
exist on debian kfreebsd.
rtapi: disable /proc for kernel 3.10+

Reportedly, classic kernel APIs we used for the /proc filesystem
have been removed in Linux 3.10.  If so, don't even try.

(untested)
hal: disable /proc for kernel 3.10+

Reportedly, classic kernel APIs we used for the /proc filesystem
have been removed in Linux 3.10.  If so, don't even try.

(untested)
rtapi_math: drop unneeded gcc version check

As documented at http://wiki.linuxcnc.org/cgi-bin/wiki.pl?MinimumSoftwareVersions
the oldest platform we're likely to target with linuxcnc 2.7 is Ubuntu 10.04
with gcc 4.4.
rtapi_math: Move inlines out of i386.h

.. otherwise the implementations are not available e.g., on x86_64 in kernel
space
fmin/fmax: Correct return value of fmin(finite, nan)

According to C99, in the case that one argmuent is nan, the other
argument is returned.  This case is likely not exercised by our code,
but someday it might be (nan/inf are only forbidden as a value on a pin
or signal; it's not forbidden internally to a realtime component)