two small fixes for PARI power series

Author: pjbruin

src/sage/rings/power_series_pari.pyx

@@ -498,7 +498,7 @@ cdef class PowerSeries_pari(PowerSeries):
         cdef pari_gen h = ~self.g
         if h.valuation(self._parent.variable_name()) < 0:
             return self._parent.laurent_series_ring()(h)
-        return PowerSeries_pari(self._parent, h, check=True)
+        return PowerSeries_pari(self._parent, h, check=False)
 
     def __neg__(self):
         """

src/sage/rings/power_series_ring.py

@@ -373,7 +373,7 @@ def PowerSeriesRing(base_ring, name=None, arg2=None, names=None,
     if name is None:
         raise TypeError, "You must specify the name of the indeterminate of the Power series ring."
 
-    key = (base_ring, name, default_prec, sparse)
+    key = (base_ring, name, default_prec, sparse, implementation)
     if PowerSeriesRing_generic.__classcall__.is_in_cache(key):
         return PowerSeriesRing_generic(*key)