As reported by https://github.com/MarlinFirmware/Marlin/pull/3182#issuecomment-222595488

Extend M421 with I and J parameters

Remove SF_ARC_FIX from G5 (Cubic B-spline).
SF_ARC_FIX is a fix for G2/G3 (arcs) where Skeinforge always produced relative instead of absolute coordinates for the endpoint of an arc.
It's very unlikely this is also a problem with Cubic B-splines. More likely is copying from the G2/G3 code.

No compromises for the manage_heater(). manage_heater() will return immediately when there is nothing to do, but needs a constant detaT to work proper.
Calling idle() only every 200ms results in a display update every ~2 seconds - that should be enough.
For the other functionalities in idle() and manage_inactivity() 200ms is a lot but hopefully works.

Minor DELTA segmentation speedup by pulling calculations out of the loop.

Idle during long arcs
to prevent from watchdog resets during high segmented fast arcs.

Saves about 2669 bytes when deactivated. (About 1% for a AT2560, about __4%__ for a AT644!)

Add a forgotten condition

Reference: https://github.com/MarlinFirmware/Marlin/pull/3713#issuecomment-218333678

Addressing #3711

- Addressing #3689, et. al.

Additional follow-up the PR #3631(Encapsulate Stepper, Planner, Endstops in singleton classes)

・Change from abort_on_endstop_hit to stepper.abort_on_endstop_hit in endstop.cpp, Marlin_main.cpp, and ultralcd.cpp
・Add include path to cardreader.h and temperature.h in endstop.cpp(for CardReader class and disable_all_heaters())
It fix compilation error when ABORT_ON_ENDSTOP_HIT_FEATURE_ENABLED and SDSUPPORT are enabled.

・Change from digipot_current() to stepper.digipot_current() in Marlin_main.cpp
・Change from digitalPotWrite() to stepper.digitalPotWrite() in Marlin_main.cpp
It fix compilation errors when HAS_DIGIPOTSS is enabled.

・Change from microstep_mode() to stepper.microstep_mode() in Marlin_main.cpp
・Change attribute of microstep_mode() from private to public in stepper.h
・Change from microstep_readings() to stepper.microstep_readings() in Marlin_main.cpp
・Change from microstep_ms() to stepper.microstep_ms() in Marlin_main.
It fix compilation errors when HAS_MICROSTEPS is enabled.

Follow-up the PR #3631(Encapsulate Stepper, Planner, Endstops in singleton classes)

plan_bed_level_matrix -> planner.bed_level_matrix in multi extruders section of Marlin_main.cpp
It probably fix the Issue #3658(plan_bed_level_matrix not declarate).

movesplanned() -> planner.movesplanned() in ADVANCED_OK section of Marlin_main.cpp
It fix compilation error when ADVANCED_OK is enabled

The fix is simple. Most changes are because of changed indendation,
bacause of leaving early for wrong tool number

- Use new `DEBUG_POS` macro for `DELTA` debug
- Neaten up `prepare_move` a smidgen
- Remove an old commented `prepare_move()` line