Bug 26591: SIP option prevcheckout_block_checkout to block checkout of previously...

Bug 26591: SIP option prevcheckout_block_checkout to block checkout of previously checked-out documents

This patchs adds a new SIP option to block checkout of previously
checked-out documents: prevcheckout_block_checkout

See the CheckPrevCheckout system preference to enable previously
checked-out verification in Koha.

Test plan:
  1) Apply this patch
  2) Enable the CheckPrevCheckout syspref (on "Do" for instance)
  3) Enable prevcheckout_block_checkout in the SIP server config file
  4) Checkout and checkin an item for a user
  5) Checkout the item again with the SIP CLI tool
  6) Check that the SIP message is "This item was previously checked out by you"
     and that the item was not checked out
  7) Disable prevcheckout_block_checkout in the SIP server config file
  8) Checkout the item again with the SIP CLI tool
  9) Check that the SIP message is "This item was previously checked out by you"
     and that the item was checked out.
 10) Prove t/db_dependent/SIP/Message.t

Signed-off-by: Kyle M Hall <kyle@bywatersolutions.com>
Signed-off-by: Martin Renvoize <martin.renvoize@ptfs-europe.com>
Signed-off-by: Jonathan Druart <jonathan.druart@bugs.koha-community.org>