The `map_free` functions were not implemented as functions but instead
as macros which also set the map to NULL. While this is most certainly
sensible in most cases, we should prefer the more obvious behavior,
namingly leaving the map pointer intact.
Furthermore, this macro has been refactored incorrectly during the
map-refactorings: the two statements are not actually grouped together
by a `do { ... } while (0)` block, as it is required for macros to
match the behavior of functions more closely. This has led to at least
one subtle nesting error in `pack-objects.c`. The following code block
```
if (pb->object_ix)
git_oidmap_free(pb->object_ix);
```
would be expanded to
```
if (pb->object_ix)
git_oidmap__free(pb->object_ix); pb->object_ix = NULL;
```
which is not what one woudl expect. While it is not a bug here as it
would simply become a no-op, the wrong implementation could lead to bugs
in other occasions.
Fix this by simply removing the macro altogether and replacing it with
real function calls. This leaves the burden of setting the pointer to
NULL afterwards to the caller, but this is actually expected and behaves
like other `free` functions.
This adds create and free callback to the git_objects_table so
that more of the creation and destruction of objects can be table
driven instead of using switch statements. This also makes the
semantics of certain object creation functions consistent so that
we can make better use of function pointers. This also fixes a
theoretical error case where an object allocation fails and we
end up storing NULL into the cache.
git.git uses an inlined hashcmp function instead of memcmp, since it
performes much better when comparing hashes (most hashes compared
diverge within the first byte).
Measurements and rationale for the curious reader:
http://thread.gmane.org/gmane.comp.version-control.git/172286
This renamed `git_khash_str` to `git_strmap`, `git_hash_oid` to
`git_oidmap`, and deletes `git_hashtable` from the tree, plus
adds unit tests for `git_strmap`.
