Bug 15721: About page does not display Apache version

Bug 15721: About page does not display Apache version

This patch changes about.pl to get version information from
C4::Context where applicable and fixes missing display of
the Apache version e.g. for Apache/2.2.22

To test:
- Without patch, open about page in staff client
- Remember contents of tab 'Server information'
  (e.g. make a screenshot)
- Apply patch
- Verify, that the About page displays the same information
  as before rsp. additionally displays Apache version if
  it was missing without patch.

Signed-off-by: Hector Castro <hector.hecaxmmx@gmail.com>
Works as described
Signed-off-by: Tomas Cohen Arazi <tomascohen@unc.edu.ar>
Signed-off-by: Brendan Gallagher brendan@bywatersolutions.com
(cherry picked from commit c2fe13c13ad286e6fc67240624eee6d95c5e7334)
Signed-off-by: Julian Maurice <julian.maurice@biblibre.com>