Rename detection using diff.renames

Clean up warnings

commit: Fix potential segfault

Dereferencing commit pointer before asserting

Fixed left shift size of int.

Simply switched the ordering of the checks in the for loop where this left
shift was being made.

blame.c: Remove unnecessary error-check and goto

In private function 'load_blob'.

Fixed compilation on Windows when using libssh2.

Reorder revert test variable decls

Oh, MSVC.

Bare naked merge and rebase

Include git2/revert.h in git2.h

Updates to cancellation logic during download and indexing of packfile.

Revert support for a single commit

Add GIT_DIFF_FIND_REMOVE_UNMODIFIED flag and fix copy detection bug

When doing copy detection, it is often necessary to include
UNMODIFIED records in the git_diff so they are available as source
records for GIT_DIFF_FIND_COPIES_FROM_UNMODIFIED.  Yet in the final
diff, often you will not want to have these UNMODIFIED records.
This adds a flag which marks these UNMODIFIED records for deletion
from the diff list so they will be removed after the rename detect
phase is over.

When FIND_COPIES is used in combination with BREAK_REWRITES for
rename detection, there was a bug where the split MODIFIED delta
was only used as a target for RENAME records and not for COPIED
records.  This fixes that, converting the split into a pair of
DELETED and COPIED deltas when that circumstance arises.

Improve iconv finding for cmake

* add FindIconv helper for CMake iconv detection
* only default using iconv to ON for MacOS
* update pkg-config generation to include iconv dependency better

fix typos in docs

posix: Solaris doesn't have strnlen either

ssh: add support for ssh-agent authentication