Revert "Enable the wincred credential helper by default for Windows users."

This reverts commit 2db3aa7c413697fdc02f5b94ebb847ee67290775.

An end user cannot unset configuration options which means that it is not
possible to disable this feature without administrative permissions. This
should only be set in the global or repository configuration files unless
the user chooses to enable this option upon installation.

Signed-off-by: Pat Thoyts <patthoyts@users.sourceforge.net>
Updated Git to v1.8.1.2

Signed-off-by: Pat Thoyts <patthoyts@users.sourceforge.net>