stablerange: add a proper debugstablerange commands This commands allows to inspect the standard stable range of a range. That should come handy.

debugobshashrange: add a --subranges option We stop displaying -everything- by default, since is is usually very large. This will help getting better timing when measuring cache effect too, since we won't need to dig out deep cache value that real life usage would not touch.

debug: rename 'debugstablerange' to 'debugobshashrange' The command is more about the 'obshashrange' computation.