usbhid-ups changes: more resiliant w/failures; scales Tripp Lite SMART1500LCDT

Had trouble getting nut to work for my new Tripp Lite SMART1500LCDT. So in best open source fashion, I hacked at it till it worked. Couple things in this pull request:

1. Scale values for some of the SMART1500LCD parameters.

2. With my hardware and kernel, usbhid-ups wouldn't run more than 10 minutes before exiting with a fatal error. This seems to be related to holding usb_claim_interface() the entire life of the program. I've refactored claim_interface/release_interface calls to be around only when work is being done. Now usbhid-ups has run for 24+ hours without issue.

3. The very nature of USB in a home means that sometimes the driver will lose communications with the UPS (accidently unplug the hub, needed a port for a camera, etc). This shouldn't be a fatal error. I've tried to detect these situations and let usbhid-ups retry gracefully. Also, at startup the UPS no longer has to be immediately present. It will keep retrying upsdrv_initups() until it finds one (only implemented for usbhid-ups, but someone could do the work for other drivers).