1. Changed thermocouple/RTD support to use new (fixed) version of
SharedSpi in CoreNG
2. PrintMonitor fixes:
- Speed up getting file info, because it was slow enough to cause Ajax
timeouts on some systems
- Reduce the number and volume of messages printed when debugging was
enabled, and send them only to the USB interface, because it was
overloading the message buffer system and causing Ajax errors
- Added separate time stats for file seeks
