hooks: add preupdate and update hooks.
preupdate run before working dir updated. can prevent update.
update run after working dir updated.
%% no changes
%% no changes
%% uncompressed contents in repo
this is a test
%% uncompress our working dir copy
this is a test
1 files updated, 0 files merged, 0 files removed, 0 files unresolved
%% uncompress our new working dir copy
this is a test