Bug 18373: Re-add UpgradeBackup.pm

Bug 18373: Re-add UpgradeBackup.pm

Bug 18028 removed the install_misc directory but
install_misc/UpgradeBackup.pm was still used by the 'upgrade' rule of
make.

Other files from install_misc were useless to it may be better not to
reintroduce this directory with only 1 file.

Test plan:
`make`
`sudo make install`
`make upgrade`

Signed-off-by: Josef Moravec <josef.moravec@gmail.com>
Signed-off-by: Marcel de Rooy <m.de.rooy@rijksmuseum.nl>
Signed-off-by: Mason James <mtj@kohaaloha.com>