filecache: use try-except for faster __dict__ lookup...
filecache: use try-except for faster __dict__ lookup
Python function call is slow, and the cost could be significant here.
$ hg perfrevset 'branch(tip)' -R mercurial
(orig) wall 0.139511 comb 0.140000 user 0.140000 sys 0.000000 (best of 66)
(this) wall 0.114195 comb 0.110000 user 0.110000 sys 0.000000 (best of 81)
