David Montenegro's patch for trial-balance (bug #144265).

[Derek Atkins]

Log Message:
-----------
David Montenegro's patch for trial-balance (bug #144265).

        * src/report/standard-reports/trial-balance.scm:
        * src/report/standard-reports/standard-reports.scm:
        * src/report/standard-reports/Makefile.am
          added Trial Balance/Work Sheet report

        * src/report/standard-reports/balance-sheet.scm:
          added drop-down choices missing in previous version
          added support for adjusting/closing entries

        * src/report/standard-reports/equity-statement.scm:
          added support for adjusting/closing entries
          fixed "For Period Covering" label
          fixed handling of unrealized gains
          investment/draw discrimination based on shares sign
          omit unrealized gains when zero

        * src/report/report-system/html-acct-table.scm:
        * src/report/report-system/html-table.scm:
          null reference bug fixes

        * src/report/report-system/report-utilities.scm:
          added utility functions for accessing splits
          and creating double-column balance HTML
          gnc:double-col,
          gnc:account-get-trans-type-balance-interval,
          gnc:account-get-pos-trans-total-interval

        * src/report/report-system/commodity-utilities.scm:
        * src/report/report-system/html-acct-table.scm:
        * src/report/report-system/report-utilities.scm:
          moved gnc:commodity-collector-commodity-count and
          gnc:uniform-commodity? into commodity-utilities.scm

        * src/report/report-system/report-system.scm:
          added some additional exports

Modified Files:
--------------
    gnucash:
        ChangeLog
    gnucash/src/report/report-system:
        commodity-utilities.scm
        html-acct-table.scm
        html-table.scm
        report-system.scm
        report-utilities.scm
    gnucash/src/report/standard-reports:
        Makefile.am
        balance-sheet.scm
        equity-statement.scm
        pnl.scm
        standard-reports.scm