[FIX] Computed opening balance was wrong in some cases when there is opening entries in the very first opening period.

In almost all cases, the entries which are in the opening periods must not be considered for the computation of the
      initial balances of partners. In one case, though they have to be considered: the opening entries in the very first year
      in the accounting. Thoses entries do not have any counterpart the previous year and have to be summed to the initial balance.
(lp:c2c-addons/6.1  rev 80.1.5)

account_financial_report_webkit/report/common_partner_reports.py

@@ -23,7 +23,9 @@
 # By using properties we will have a more simple signature in fuctions
 
 from collections import defaultdict
+from datetime import datetime
 
+from openerp.tools import DEFAULT_SERVER_DATE_FORMAT
 from common_reports import CommonReportHeaderWebkit
 
 
@@ -47,6 +49,51 @@ class CommonPartnersReportHeaderWebkit(CommonReportHeaderWebkit):
                                                     exclude_reconcile=exclude_reconcile,
                                                     partner_filter=partner_filter)
 
+    def _get_first_special_period(self):
+        """
+        Returns the browse record of the period with the `special` flag, which
+        is the special period of the first fiscal year used in the accounting.
+
+        i.e. it searches the first fiscal year with at least one journal entry,
+        and it returns the id of the first period for which `special` is True
+        in this fiscal year.
+
+        It is used for example in the partners reports, where we have to include
+        the first, and only the first opening period.
+
+        :return: browse record of the first special period.
+        """
+        move_line_obj = self.pool.get('account.move.line')
+        first_entry_id = move_line_obj.search(
+            self.cr, self.uid, [], order='date ASC', limit=1)
+        # it means there is no entry at all, that's unlikely to happen, but
+        # it may so
+        if not first_entry_id:
+            return
+        first_entry = move_line_obj.browse(self.cr, self.uid, first_entry_id[0])
+        fiscalyear = first_entry.period_id.fiscalyear_id
+        special_periods = [period for period in fiscalyear.period_ids if period.special]
+        # so, we have no opening period on the first year, nothing to return
+        if not special_periods:
+            return
+        return min(special_periods,
+                   key=lambda p: datetime.strptime(p.date_start, DEFAULT_SERVER_DATE_FORMAT))
+
+    def _get_period_range_from_start_period(self, start_period, include_opening=False,
+                                            fiscalyear=False,
+                                            stop_at_previous_opening=False):
+        """We retrieve all periods before start period"""
+        periods = super(CommonPartnersReportHeaderWebkit, self).\
+                _get_period_range_from_start_period(
+                        start_period,
+                        include_opening=include_opening,
+                        fiscalyear=fiscalyear,
+                        stop_at_previous_opening=stop_at_previous_opening)
+        first_special = self._get_first_special_period()
+        if first_special:
+            periods.append(first_special.id)
+        return list(set(periods))
+
     def _get_query_params_from_periods(self, period_start, period_stop, mode='exclude_opening'):
         # we do not want opening period so we exclude opening
         periods = self.pool.get('account.period').build_ctx_periods(self.cr, self.uid, period_start.id, period_stop.id)