Accept outside ENABLE_DEBUG_MONITOR settings.

You can now specify ENABLE_DEBUG_MONITOR setting from outside the
makefile and it will only be set to 0 if another value wasn't
provided on the make command line or environment variable.  This allows
it to be specified in builds kicked off from Eclipse.
Remove iprintf() call from spi.cpp

People were noticing that MRI was halting and waiting for GDB to attach
immediately at startup when configured for full debugging mode.  This
was because output was being sent to stdout and MRI was waiting to
redirect it to GDB's console.  I tracked this down to an
iprintf("\n") call in spi.cpp so I commented it out like the rest of
the iprintf() calls in this file.
added max_pwm to temperaturecontrol
Merge branch 'edge' of github.com:arthurwolf/Smoothie into edge
SDCard: implement busy flag
USB: run USB stack from idle event instead of via interrupts
Module: use macros for event definitions to ensure consistency
Module: don't sign all modules up for ON_CONFIG_RELOAD- they don't all use the event.
Module Events: remove on_stepper_wake_up event as it was unused
Merge remote-tracking branch 'upstream/edge' into working
Revert "SDCard: implement busy flag"

This reverts commit cab8989342ca28ebcdf018abb56d89fa9b5bc822.
Revert "Revert "SDCard: implement busy flag""

This reverts commit 3d99be483447eb24d52580643c38c6b2661567fd.
USB: work around OSX behaviour where if the device disconnects and quickly reconnects, it assumes it's the same device instead of checking
USB: ensure Connect pin is set up before disconnect delay
Merge remote-tracking branch 'upstream/edge' into working
_sbrk() check for overflow past MSP.

Make sure that a dynamic memory allocation won't exceed the current top
of stack.  It is still possible for stack to grow down into heap.
Merge remote-tracking branch 'upstream/edge' into working
Gcode: Ensure std::string operations don't incur allocations
Merge pull request #94 from bgamari/fixes

Gcode: Ensure std::string operations don't incur allocations
Merge remote-tracking branch 'upstream/edge' into working