Bug 8271 teach SIPServer.pm to set its own lib path

Bug 8271 teach SIPServer.pm to set its own lib path

SIPServer.pm requires that C4/SIP is added to its lib
path This has been done by passing this directory
to it via -I. By using FindBin it can set the path
for itself correctly. This will also work if the C4/SIP
directory tree is moved to a non-standard location
Removed the now redundant -I. from sip_run.sh

Added a variable to sip_run.sh for the koha tree to
highlight a problem with the script if you have multiple
directories in the PERL5LIB environment variable

Signed-off-by: Chris Cormack <chris@bigballofwax.co.nz>
Signed-off-by: Paul Poulain <paul.poulain@biblibre.com>