Simplify the PinForm.clean method

I have a gut feeling that we could refactor some code out of this method, but for now I'll just clean it up a bit.

pinry/pins/forms.py

@@ -4,20 +4,12 @@ from .models import Pin
 
 
 class PinForm(forms.ModelForm):
-    url = forms.CharField(label='url', required=False)
+    url = forms.CharField(required=False)
     image = forms.ImageField(label='or Upload', required=False)
 
     class Meta:
         model = Pin
-        fields = ['url', 'description', 'tags']
-
-    def check_if_image(self, data):
-        # Test file type
-        image_file_types = ['png', 'gif', 'jpeg', 'jpg']
-        file_type = data.split('.')[-1]
-        if file_type.lower() not in image_file_types:
-            raise forms.ValidationError("Requested URL is not an image file. "
-                                        "Only images are currently supported.")
+        fields = ['url', 'image', 'description', 'tags']
 
     def clean(self):
         cleaned_data = super(PinForm, self).clean()
@@ -26,26 +18,25 @@ class PinForm(forms.ModelForm):
         image = cleaned_data.get('image')
 
         if url:
-            self.check_if_image(url)
+            image_file_types = ['png', 'gif', 'jpeg', 'jpg']
+            if not url.split('.')[-1].lower() in image_file_types:
+                raise forms.ValidationError("Requested URL is not an image file. "
+                                            "Only images are currently supported.")
+            try:
+                Pin.objects.get(url=url)
+                raise forms.ValidationError("URL has already been pinned!")
+            except Pin.DoesNotExist:
+                pass
+            protocol = url.split(':')[0]
+            if protocol not in ['http', 'https']:
+                raise forms.ValidationError("Currently only support HTTP and "
+                                            "HTTPS protocols, please be sure "
+                                            "you include this in the URL.")
             try:
                 Pin.objects.get(url=url)
                 raise forms.ValidationError("URL has already been pinned!")
             except Pin.DoesNotExist:
-                protocol = url.split(':')[0]
-                if protocol == 'http':
-                    opp_url = url.replace('http://', 'https://')
-                elif protocol == 'https':
-                    opp_url = url.replace('https://', 'http://')
-                else:
-                    raise forms.ValidationError("Currently only support HTTP and "
-                                                "HTTPS protocols, please be sure "
-                                                "you include this in the URL.")
-
-                try:
-                    Pin.objects.get(url=opp_url)
-                    raise forms.ValidationError("URL has already been pinned!")
-                except Pin.DoesNotExist:
-                    pass
+                pass
         elif image:
             pass
         else: