Pulse Difference input processing, handle signed integer

Instead of silently ignoring negative values passed into pulse_diff(),
convert them to unsigned integer. Pulses should always be positive.
Dashboard: Fix selecting item to add under Chrome Mac

Instead of using click(), use change().

http://stackoverflow.com/questions/8295642/jquery-function-doesnt-work-o
n-chrome-on-mac-but-works-on-chrome-on-win-7-and

http://stackoverflow.com/questions/11384389/why-does-select-box-on-mac-c
hrome-doesnt-respond-to-click-event

Refs #21
Merge pull request #23 from oscarcarlsson/master

Pulse Difference input processing, handle signed integer