refs #335 Fix units name displayed for differential values in ZSUM referentials

ZSUM referentials are subsets of Relative and Quantitative referentials.
Differential values are not ZSUM values and must display the units of their parent referential.

src/sakia/core/money/quant_zerosum.py

@@ -2,6 +2,7 @@ from PyQt5.QtCore import QCoreApplication, QT_TRANSLATE_NOOP, QLocale
 from . import Quantitative
 import asyncio
 
+
 class QuantitativeZSum:
     _NAME_STR_ = QT_TRANSLATE_NOOP('QuantitativeZSum', 'Quant Z-sum')
     _REF_STR_ = QT_TRANSLATE_NOOP('QuantitativeZSum', "{0} Q0 {1}")
@@ -22,7 +23,7 @@ class QuantitativeZSum:
 
     @classmethod
     def diff_units(cls, currency):
-        return QuantitativeZSum.units(currency)
+        return Quantitative.units(currency)
 
     @asyncio.coroutine
     def value(self):
@@ -63,4 +64,4 @@ class QuantitativeZSum:
     @asyncio.coroutine
     def diff_localized(self, units=False, international_system=False):
         localized = yield from Quantitative(self.amount, self.community, self.app).localized(units, international_system)
-        return localized
+        return localized
\ No newline at end of file

src/sakia/core/money/quantitative.py

 from PyQt5.QtCore import QCoreApplication, QT_TRANSLATE_NOOP, QObject, QLocale
 import asyncio
 
+
 class Quantitative():
     _NAME_STR_ = QT_TRANSLATE_NOOP('Quantitative', 'Units')
     _REF_STR_ = QT_TRANSLATE_NOOP('Quantitative', "{0} {1}{2}")

src/sakia/core/money/relative.py

 from PyQt5.QtCore import QObject, QCoreApplication, QT_TRANSLATE_NOOP, QLocale
 import asyncio
 
-class Relative():
+
+class Relative:
     _NAME_STR_ = QT_TRANSLATE_NOOP('Relative', 'UD')
     _REF_STR_ = QT_TRANSLATE_NOOP('Relative',  "{0} {1}UD {2}")
     _UNITS_STR_ = QT_TRANSLATE_NOOP('Relative',  "UD {0}")

src/sakia/core/money/relative_zerosum.py

@@ -22,7 +22,7 @@ class RelativeZSum:
 
     @classmethod
     def diff_units(cls, currency):
-        return RelativeZSum.units(currency)
+        return Relative.units(currency)
 
     @asyncio.coroutine
     def value(self):