Progress callbacks

reset changes for merge

git_indexer_stats and friends -> git_transfer_progress*

Also made git_transfer_progress members more sanely
named.

Use libcrypto's SHA-1 implementation when linking to it

libcryto's SHA-1 implementation is measurably better than the one that
ships with the library. If we link to it for HTTPS support already,
use that implementation instead.

Testing on a ~600MB of the linux repository, this reduces indexing
time by 40% and removes the hashing from the top spot in the perf
output.

Add git_config_level support when handling config files

Added `struct git_config_entry`: a git_config_entry contains the key, the value, and the config file level from which a config element was found.
Added `git_config_open_level`: build a single-level focused config object from a multi-level one.

We are now storing `git_config_entry`s in the khash of the config_file

This can occur after a manual modification of a config file.

Save the autotag configuration for remotes

More orphaned head love

blob: do not create temp files in the current path

 - make sure temporary streamed blobs are created under the
.git/objects folder and not in the current path, whatever it is.

 - do not make the name of the temp file depend on the hintpath.

Also, now only reporting checkout progress for files that
are actually being added or removed.

The fetch code takes advantage of this to implement a
progress callback every 100kb of transfer.

Also implemented in the git2 example.

git_index_read_tree() was exposing a parameter to provide the user with
a progress indicator. Unfortunately, due to the recursive nature of the
tree walk, the maximum number of items to process was unknown. Thus,
the indicator was only counting processed entries, without providing
any information how the number of remaining items.