LP 1198465: Initial tests for conditional negative balances

LP 1198465: Initial tests for conditional negative balances

This is a first commit of work-in-progress for testing the conditional
negative balances features.  It covers 9 of the 14 test cases listed
here (as of today):

http://evergreen-ils.org/dokuwiki/doku.php?id=qa:billing_test_cases

TODO:
- The test is currently an SQL setup file plus a Perl live test file.
  One simple improvement would be to switch the setup process to
  cstore calls within the Perl test file.  This would be both more
  contained and more robust.
- A second step to more advanced and useful tests would be to use
  higher-level API calls to create portions of the setup rather than
  doing everthing manually.  However, some test conditions cannot be
  reasonably setup with the normal API calls (e.g. bills of a specific
  age, or bills using a legacy format no longer generated by current
  code), so certain areas will likely always require direct
  manipulation.

Signed-off-by: Daniel Wells <dbw2@calvin.edu>