FIX: imshow arguments should be popped before passing upstream

We have extra keyword arguments in Cartopy that can't be passed
upstream to Matplotlib, so remove them from the keyword arguments
before going into any possible methods.

lib/cartopy/mpl/geoaxes.py

@@ -1279,7 +1279,9 @@ def imshow(self, img, *args, **kwargs):
                           x0 - eps <= extent[1] <= x1 + eps and
                           y0 - eps <= extent[2] <= y1 + eps and
                           y0 - eps <= extent[3] <= y1 + eps))
-
+        # Make sure we are popping the regrid_shape before calling any
+        # upstream imshow methods.
+        regrid_shape = kwargs.pop('regrid_shape', 750)
         if (transform is None or transform == self.transData or
                 same_projection and inside_bounds):
             result = super().imshow(img, *args, **kwargs)
@@ -1298,7 +1300,6 @@ def imshow(self, img, *args, **kwargs):
                                  'handle a %s in imshow.' % type(transform))
 
             target_extent = self.get_extent(self.projection)
-            regrid_shape = kwargs.pop('regrid_shape', 750)
             regrid_shape = self._regrid_shape_aspect(regrid_shape,
                                                      target_extent)
             # Lazy import because scipy/pykdtree in img_transform are only

lib/cartopy/tests/mpl/test_images.py

@@ -139,6 +139,17 @@ def test_imshow_wrapping():
     assert ax.get_xlim() == (-180, 180)
 
 
+def test_imshow_arguments():
+    """Smoke test for imshow argument passing in the fast-path"""
+    ax = plt.axes(projection=ccrs.PlateCarree())
+    # Set the regrid_shape parameter to ensure it isn't passed to Axes.imshow()
+    # in the fast-path call to super()
+    ax.imshow(np.random.random((10, 10)), transform=ccrs.PlateCarree(),
+              extent=(-180, 180, -90, 90), regrid_shape=500)
+
+    assert ax.get_xlim() == (-180, 180)
+
+
 def test_imshow_rgba():
     # tests that the alpha of a RGBA array passed to imshow is set to 0
     # instead of masked