contrib: make perf.py use absolute_import

largefiles: replace invocation of os.path module by vfs in lfutil.py Replaces invocations os.path functions to methods in vfs. Unfortunately (in my view) this makes code less readable, because instead of using clear variable names with path it needs to replace them with vfs(..). I need guidance how to make such transition look more readable. For example in this patch there is example with few places with wvfs.join(standindir), standindir before this patch was absolute path, in this it is changed to relative because it is used also in expression wvfs.join(standindir, pat).

largefiles: replace invocation of os.path module by vfs in lfcommands.py

cache: rebuild branch cache from scratch when inconsistencies are detected This should recover automatically from some corruptions that for unknown reasons are seen in the wild.