Added checkbox "Don't suspend pinned tabs"
Changed version in manifest from 4.74 to 4.75
v4.76   2013-05-25
- improv:   URLs starting with chrome-devtools: are never suspended
- bugfix:   activating a tab does not refresh its timeout
- bugfix:   'Suspend this tab' could potentially suspend more than one
tab
- internal: added extra logging for easier debugging
- internal: some refactoring in background.js
v4.77   2013-05-25
- bugfix:   switched off debug mode that was causing very quick
suspending
v4.80   2013-10-01
- feature:  suspend multiple selected (highlighted) tabs
Merge branch 'pr/38'

Conflicts:
	background.js