Changes to CMake for packaging

Fix env variable tests with new Win32 path rules

Rename INSTALL_INC and INSTALL_BIN to INCLUDE_INSTALL_DIR and
BIN_INSTALL_DIR, which are more commonly used. This is also
consistent with the variable for the library path which is
already LIB_INSTALL_DIR.

The new Win32 global path search was not working with the
environment variable tests.  But when I fixed the test, the new
codes use of getenv() was causing more failures (presumably because
of caching on Windows ???).  This fixes the global file lookup to
always go directly to the Win32 API in a predictable way.

Add error GIT_EORPHANEDHEAD

Update README because vmg is @vmg.

Enhance test coverage

Update clar and add reliable rename for Win32

revparse: properly handle refnames containing a @

Fix #994

remote: support fetch cancelation

Introduce git_remote_stop() which sets a variable that is checked by
the fetch process in a few key places. If this is variable is set, the
fetch is aborted.

Support TYPECHANGE records in status and adjust checkout accordingly

Fixed no-submodule speedup of new checkout code.  Fixed missing
final update to progress (which may go away, I realize).  Fixed
unused structure in header and incorrect comment.

Separated git_strarray from common.h.  Added doxy comments.

Skip the third pass of checkout (where submodules are checked out)
if the earlier passes found no submodules to be checked out.

Incremental improvements to pack-objects logic

Incorporate feedback for incr. improvements to pack-objects

Support pthread_cond_* on Win32

Not found means not found, and the other way around.