refs: append to the HEAD reflog when updating the current branch

Add a few projects to the list

When we update the current branch, we must also append to HEAD's reflog
to keep them in sync.

This is a bit of a hack, but as git.git says, it covers 100% of
default cases.

This is not something anybody would ever do; removing HEAD makes the
.git/ directory no longer be a repository, so we wouldn't be expected to
handle such a situation.

Fix pqueue sort boundary condition bug

If the pqueue comparison fn returned just 0 or 1 (think "a<b")
then the sort order of returned items could be wrong because there
was a "< 0" that really needed to be "<= 0".  Yikes!!!

Add git_submodule_resolve_url()

corrected typo in error message

Update clar to e1990d6

Rename options structures

Add a tag example

Fun with memory access

Plug leaks

We look up a reference in order to figure out if it's the current
branch, which we need to free once we're done with the check.

As a bonus, only perform the check when we're passed the force flag, as
it's a useless check otherwise.

We can make use of git_object_dup to use refcounting instead of pointer
comparison to make sure we don't free the caller's object.

This also lets us simplify the case for '~0' which is now just an
assignment instead of looking up the object we have at hand.

Combinations of connect + fetch can call local_open multiple
times. Detect this and skip the initialization stage.

Previously the hunk_byfinalline_search_cmp function was called with different
data types (size_t and uint32_t) for the key argument but expected only the
former resulting in an invalid memory access when passed the latter on a 64 bit
machine.

The following patch makes sure that the function is called and works with the
same type (size_t).

Update clar to a0b00f0

MSVC doesn't like declaring variables in the middle of a block, so make
sure we only declare variables at the beginning of a block.

Revert pull request #1997

Fix GIT_MERGE_OPTS_INIT on MSVC.

Function-based options initializers

examples/diff:Add the shortstat flag to examples/diff.c

The basic structure of each function is courtesy of arrbee.

Add ODB API to check for existence by prefix and object id shortener