Revert "motion: introduce motion.ferror-mode"

This reverts commit 203e2c4bfd9037f81e6a70c8d51c40519a7eae47.
Make pid's idea of following error match motion's

Motion generates a new commanded position each servo cycle.  It expects the
machine to move such that at the next period, it will be at that new target.
It calculates ferror accordingly (this period's feedback vs last period's
command.)

Until now, pid didn't agree about what ferror meant: it would read the
commanded and feedback positions simulatneously and call that difference the
following error.  This made it disagree with motion by the distance moved in
one period, which gave an ferror discrepancy proportional to velocity.

Unfortunately this fix has to be optional, at least in the release branch,
because it will affect existing pid tunings.
Document new pid pin
French doc. update

Signed-off-by: Francis Tisserant <tissf@free.fr>
fix rebranding mistake
detect "sticky" ID bits on IEEE-1284 bus
print INFO message if no boards found
latencyhistogram, latencybins.comp

latencyhistogram: script to plot latencies using hal.
latencybins.comp: supporting .comp that measures latency
                  between thread invocations and accumulates
                  counts in bins.
ignore new generated file
fix bogus execute permissions on a few comps
French doc. update pictures

Signed-off-by: Francis Tisserant <tissf@free.fr>
French doc. update pictures

Signed-off-by: Francis Tisserant <tissf@free.fr>
Docs: re-branding update image

Signed-off-by: John Thornton <jthornton@gnipsel.com>
Docs: re-branding update image

Signed-off-by: John Thornton <jthornton@gnipsel.com>
latencyhistogram: fix bins computation
emcmodule.cc: fail gracefully for linuxcnc.ini()

avoid segfault in Ini_dealloc()

before patch:
      $ python -c 'import linuxcnc; x=linuxcnc.ini()'
      Segmentation fault (core dumped)

after:
      $ python -c 'import linuxcnc; x=linuxcnc.ini()'
      Traceback (most recent call last):
        File "<string>", line 1, in <module>
      TypeError: function takes exactly 1 argument (0 given)

similar behavior for  x=linuxcnc.ini(None)
Don't leak file descriptors or memory when abused

It's possible to call Ini_init multiple times, don't leak a new IniFile
or a file descriptor each time.

In Ini_dealloc it's still necessary to PyObjectDel self; it's defined as
OK (a no-op) to delete a NULL pointer, so the delete statement doesn't
need to be guarded by the test.
docs: simplify a link in the html front page

index.html and gcode.html live in the same directory: the root of the
generated html tree.  So there's no need to bounce around directories
when linking.
docs: clarfiy G53

"absolute coordinates" might be confused with G90, calling it the "machine
coordinate system" seems clearer.
docs: remove a bogus entry in the M-code TOC

Looks like a silly cut-n-paste error.