Solve issue of strange warning message

Recognise the names given by SANS2D instruments for the bank detectors,
and explain better the warning message.

re #6982

Code/Mantid/scripts/SANS/isis_reduction_steps.py

@@ -1456,13 +1456,13 @@ def getPixelCorrFile(self, detector ):
           override CalculateNorm.
         """
         detector = detector.upper()
-        if detector in ("FRONT","HAB","FRONT-DETECTOR-BANK"):
+        if detector in ("FRONT","HAB","FRONT-DETECTOR-BANK", "FRONT-DETECTOR"):
             return self._high_angle_pixel_file
-        elif detector in ("REAR","MAIN","MAIN-DETECTOR-BANK",""):
+        elif detector in ("REAR","MAIN","MAIN-DETECTOR-BANK","", "REAR-DETECTOR"):
             return self._low_angle_pixel_file
         else :
-            logger.warning("ASK GETPIXELCORRFILE WITHOUT ARGUMENT: + "+ str(detector))
-            return self._pixel_file        
+            logger.warning("Request of pixel correction file with unknown detector ("+ str(detector)+")")
+            return self._pixel_file
 
     def calculate(self, reducer, wave_wks=[]):
         """