Log Message:
gnucash: update to 2.6.18.1.

2.6.18 - 24 September 2017

The following bugs are fixed:
     Bug 644898 - Calendar of upcoming SXes has various display issues
     Bug 647805 - Interdependent report options fail to change state after
                  using apply for a limited number of times.
     Bug 771246 - Set Invoice/Bill items date correctly from imported CSV.
     Bug 784284 - unifying "Clear the entry." tooltip on Loan Repayment
                  Calculator
     Bug 787479 - Persian currency symbol is doubled.

Other repairs not marked as bugs in git:
      Added Catalan Accounts for the New Account Assistant
      Fixed errors from loading init.py.
      Run the python bindings tests in a CMake build.
      Implement dist, distcheck, and uninstall targets for CMake build.

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