Make sure we set the output parameter to a value.

When deflating data, we might need to grow the buffer. Currently we
add a guess on top of the currently-allocated buffer size.

When we re-use the buffer, it already has some memory allocated; adding
to that means that we always grow the buffer regardless of how much we
need to use.

Instead, increase on top of the currently-used size. This still leaves
us with the allocated size of the largest object we compress, but it's a
minor pain compared to unbounded growth.

This fixes #2285.

Fire progress and update tips callbacks also for pushes.

Improve stash and checkout for ignored + untracked items

Merge checkout strategy

When considering status of untracked directories, if we find an
explicitly ignored item, even if it is a directory, treat the
parent as an IGNORED item.  It was accidentally being treated as
an EMPTY item because we were not looking into the ignored subdir.

The current FETCH_HEAD parsing code assumes that a quote must end the
branch name. Git however allows for quotes as part of a branch name,
which causes us to consider the FETCH_HEAD file as invalid.

Instead of searching for a single quote char, search for a quote char
followed by SP, which is not a valid part of a ref name.