obsstore: cache size computation for fm1 node
We have two different types of node type (sha1 and sha256, only sha1 is used
now) and therefor different sizes for them. We now compute the value once
instead of redoing the computation every loop. This has no visible performance
impact.
$ hg init
$ touch unknown
$ touch a
$ hg add a
$ hg ci -m "1"
$ touch b
$ hg add b
$ hg ci -m "2"
Should show unknown
$ hg status
? unknown
$ hg revert -r 0 --all
removing b
Should show unknown and b removed
$ hg status
R b
? unknown
Should show a and unknown
$ ls
a
unknown