Fix for a wrong checksum truncation for certain commands

Positioning of string terminator to truncate checksum from the commands
M23, M28, M30, M32, M928 and M117 was off by one, causing the last
letter of the actual command to be truncated instead of just the
checksum.

In case of the SD commands this caused checksummed commands targeting
existing files to fail since the last letter of the filename was
truncated.

In case of M117 this caused the last given letter not to be displayed.

This patch fixes the off-by-one error and sets the null terminator
on the exact position of the * starting the checksum instead of the
character before that.
Merge pull request #1017 from foosel/fix/checksum_truncation_bug

Fix for a wrong checksum truncation for certain commands
Updated README with RigidBot specific comments at the top
Fixed default motherboard in Configuration.h (should be set in Makefile, not here)
Added LiquidCrystalFast_Mod from RigidBot code
Added Arduino hardware definition in Makefile for RigidBoard
Allow longer wait for status response in Sd2Card.cpp
Increased FAT long filename support buffer 26 -> 39 characters
Typo in pins.h for RigidBot
Added rigidlcd (ultralcd modification with print-from-USB) -- needs
Makefile changes to be "selectable"
Merge pull request #3 from gregrebholz/Marlin_v1

Almost there
Merge remote-tracking branch 'upstream/Marlin_v1' into Marlin_v1

Catching up with Marlin v1
Successful compile of RepRap Discount Full Graphic LCD and RigidPanel
LCD.  Code cleanup for Marlin pull request.
Merge pull request #4 from gregrebholz/Marlin_v1

Needs testing
Fixed RigidPanel LCD.  Created predefined mechanical settings for
RigidBot.  Fixed typo in STEPPER_RESET_FIX.
Fixed non-RigidBot compile error
Fixed incorrect build volumes for RigidBot.  Added automated build
script for RigidBot Community Edition permutations
Merge pull request #5 from gregrebholz/Marlin_v1

RigidPanel LCD and Full Graphic LCD support
hijacking MOSI to function as CS, fix HEAT_INTERVAL bug
update configuration settings