Fixed problem whereby gcode files printed from SD card that used lots of
small fast moves in sequence would print jerkily if a network cable had
not been connected since reset.
Fixed problem whereby object height and filament needed were not
retrieved from the SD card file to be printed if the filename contained
spaces.
Added support for deprecated M190 command, because slic3r appears to
generate it sometimes
Added support for M564 command to allow movement without limits, copied
from RepRapPro dev branch
Fixed bug in file handling that affected SD card pause/resume
operations. Merged changes from zombiepantslol to allow a height to be
set for a Z endstop switch. Reverted to blocking USB I/O but only for
debug and M503 output. Added return codes for file close and seek
operations. Increased the size of the tail of the file that we scan for
G1 Z commands from 32K to nearly 200K.
Changed network startup to avoid long delay if no network cable is
connected
Enable DHCP support if IP address is configured as 0.0.0.0 (not working
yet)
Move thermistor parameters to M305, added parameter to configure series
resistance
Added B and W PID parameters
