fsmonitor: option to allow fsmonitor to run against network-mounted repos

fsmonitor: option to allow fsmonitor to run against network-mounted repos

Though perhaps not common, there are use cases where users have large,
network-mounted repos. Having the ability to run fsmonitor against
network paths would benefit those users.

Most modern Samba-based filers have the necessary support to enable
fsmonitor on network-mounted repos. As a first step towards enabling
fsmonitor to work against network-mounted repos, introduce a
configuration option, 'fsmonitor.allowRemote'. Setting this option to
true will override the default behavior (erroring-out) when a
network-mounted repo is detected by fsmonitor.

Signed-off-by: Eric DeCosta <edecosta@mathworks.com>
Signed-off-by: Junio C Hamano <gitster@pobox.com>