LP#1638377: Allow perl to be installed in non-standard locations

LP#1638377: Allow perl to be installed in non-standard locations

Add --with-perlbase configure option to specify
an alternative location for installing the Perl modules. This
can be useful for setups that want to run the Perl modules
from a shared filesystem or environments that need to run
multiple versions of OpenSRF simultaneously.

Users of --with-perlbase are responsible for ensuring that
PERL5LIB is set appropriately.

To test
-------
[1] Use --with-perlbase during the configure step, e.g.,

    ./configure --with-perlbase /tmp/perl

[2] Run make; make check; sudo make install
[3] Verify that the Perl modules are installed under
    /tmp/perl.
[4] Make a change to a Perl source file, then
    go to src/perlmods, then run sudo ./Build install. Verify
    that it remembers the --with-perlbase directory
    and installs the updated module there.

Signed-off-by: Mike Rylander <mrylander@gmail.com>
Signed-off-by: Chris Sharp <csharp@georgialibraries.org>