Disabled CoreImage filters on iOS 8.x due to runtime mapping issue wi…

…th CIContext.

See the following Stack Overflow thread for more info:

- http://tinyurl.com/jh26j6m

Source/ImageFilter.swift

@@ -289,6 +289,7 @@ public struct CircleFilter: ImageFilter {
 #if os(iOS) || os(tvOS)
 
 /// The `CoreImageFilter` protocol defines `parameters`, `filterName` properties used by CoreImage.
+@available(iOS 9.0, *)
 public protocol CoreImageFilter: ImageFilter {
     /// The filter name of the CoreImage filter.
 	var filterName: String { get }
@@ -297,6 +298,7 @@ public protocol CoreImageFilter: ImageFilter {
     var parameters: [String: Any] { get }
 }
 
+@available(iOS 9.0, *)
 public extension ImageFilter where Self: CoreImageFilter {
 	/// The filter closure used to create the modified representation of the given image.
 	public var filter: (Image) -> Image {
@@ -310,6 +312,7 @@ public extension ImageFilter where Self: CoreImageFilter {
 }
 
 /// Blurs an image using a `CIGaussianBlur` filter with the specified blur radius.
+@available(iOS 9.0, *)
 public struct BlurFilter: ImageFilter, CoreImageFilter {
     /// The filter name.
     public let filterName = "CIGaussianBlur"

Source/UIImage+AlamofireImage.swift

@@ -275,6 +275,7 @@ import CoreImage
 
 // MARK: - Core Image Filters
 
+@available(iOS 9.0, *)
 extension UIImage {
     /// Returns a new version of the image using a CoreImage filter with the specified name and parameters.
     ///

Tests/ImageFilterTests.swift

@@ -205,6 +205,8 @@ class ImageFilterTestCase: BaseTestCase {
     }
 
     func testThatBlurFilterReturnsCorrectFilteredImage() {
+        guard #available(iOS 9.0, *) else { return }
+
         // Given
         let image = self.image(forResource: "unicorn", withExtension: "png")
         let filter = BlurFilter(blurRadius: 8)

Tests/UIImageTests.swift

@@ -340,6 +340,8 @@ class UIImageTestCase: BaseTestCase {
     // MARK: - Core Image Filters
 
     func testThatImageWithAppliedGaussianBlurFilterReturnsBlurredImage() {
+        guard #available(iOS 9.0, *) else { return }
+
         // Given
         let parameters: [String: Any] = ["inputRadius": 8]
 
@@ -358,6 +360,8 @@ class UIImageTestCase: BaseTestCase {
     }
 
     func testThatImageWithAppliedSepiaToneFilterReturnsSepiaImage() {
+        guard #available(iOS 9.0, *) else { return }
+
         // Given, When
         let sepiaImage = unicornImage.af_imageFiltered(withCoreImageFilter: "CISepiaTone")
 
@@ -371,6 +375,8 @@ class UIImageTestCase: BaseTestCase {
     }
 
     func testThatInvalidCoreImageFilterReturnsNil() {
+        guard #available(iOS 9.0, *) else { return }
+
         // Given
         let filterName = "SomeFilterThatDoesNotExist"