Sha1 lookup and GIT_USE_LOOKUP

Hi, I noticed in find_pack_entry_one the use of the environment variable GIT_USE_LOOKUP, which does not seem to be used anywhere else in git or even in the tests.

Obviously, it determines whether or not a simple binary search or the sha1_entry_pos method (which is apparently some kind of improved binary search) should be used to retrieve the offset of an object (given its sha1) in a pack. Since this environment variable is not set by default, git will always use a simple binary search, won't it ?

Also, when searching for a sha1 given a sha1 prefix, among packed objects, find_short_packed_object also does a simple binary search. Wouldn't it be simpler to just use the sha1_entry_pos method ?

Thanks

-- Marc Pegon