Redir refactor

Initial Implementation of progress reports during push

Never consider submodules for stashing

...before the helper's cleanup method tries to delete their files.

Fix x86/x64 size_t related warnings

This adds the basics of progress reporting during push. While progress
for all aspects of a push operation are not reported with this change,
it lays the foundation to add these later. Push progress reporting
can be improved in the future - and consumers of the API should
just get more accurate information at that point.

The main areas where this is lacking are:

1) packbuilding progress: does not report progress during deltafication,
   as this involves coordinating progress from multiple threads.

2) network progress: reports progress as objects and bytes are going
   to be written to the subtransport (instead of as client gets
   confirmation that they have been received by the server) and leaves
   out some of the bytes that are transfered as part of the push protocol.
   Basically, this reports the pack bytes that are written to the
   subtransport. It does not report the bytes sent on the wire that
   are received by the server. This should be a good estimate of
   progress (and an improvement over no progress).

Remove leading newlines from commit message

Fix libgit2/libgit2sharp#522

Add refdb.h to git2.h, reorder git2.h sanely

...and have that call manage replaced memory in the output structure.

Win32: handle http->https redirects

Bring error handling docs up to date

The error handling docs date back to the early error redesign
work and don't match up with the route we actually took.  This
brings them in line with actual practice both for external users
and internal implementors, and notes some of the exceptions and
possible bugs.

That's the refdb, it's not the odb...

Cleaned up some tables in checkout-internals doc

Fixed formatting of diff-internals.md

Indentation for lists was not working correctly.

The markdown wasn't rendering correctly.

Make tests pass if XDG config exists

Alternative fix for cross protocol redirects

The subtransport path was relying on pointing to data owned by
the remote which meant that after a redirect, the updated path
was getting lost for future requests.  This updates the http
transport to strdup the path and maintain its own lifetime.

This also pulls responsibility for parsing the URL back into the
http transport and isolates the functions that parse and free that
connection data so that they can be reused between the initial
parsing and the redirect parsing.

Ignore files that disappear while iterating

On occasion, files can disappear while we're iterating the
filesystem, between calls to readdir and stat.  Let's pretend
those didn't exist in the first place.