Things not done because probably disruptive:
* kmod filesystem string
* sysctl/debugfs/trace
* metrics names
* xmon instance names
Some of these might be renamed too, but starting with a relatively
safe set.
Fixes#32. This also involves some reworking of the block request machinery
to make it more robust and faster. The scrubbing is done assuming that
the overwhelming majority of block checking will go through.
