Do not enable webp when not explicitly activated by a macro (fix #415)

@@ -806,6 +806,7 @@
 				GCC_OPTIMIZATION_LEVEL = 0;
 				GCC_PREPROCESSOR_DEFINITIONS = (
 					"DEBUG=1",
+                                        "SD_WEBP=1",
 					"$(inherited)",
 				);
 				GCC_SYMBOLS_PRIVATE_EXTERN = NO;
@@ -837,6 +838,7 @@
 				ALWAYS_SEARCH_USER_PATHS = NO;
 				ARCHS = "$(ARCHS_STANDARD_32_BIT)";
 				COPY_PHASE_STRIP = YES;
+				GCC_PREPROCESSOR_DEFINITIONS = "SD_WEBP=1";
 				GCC_TREAT_WARNINGS_AS_ERRORS = YES;
 				GCC_WARN_64_TO_32_BIT_CONVERSION = YES;
 				GCC_WARN_ABOUT_MISSING_FIELD_INITIALIZERS = YES;

@@ -25,10 +25,12 @@
         image = [[UIImage alloc] initWithData:data];
     }
 
+#ifdef SD_WEBP
     if (!image) // TODO: detect webp signature
     {
         image = [UIImage sd_imageWithWebPData:data];
     }
+#endif
 
     return image;
 }

@@ -6,6 +6,7 @@
 //  Copyright (c) 2013 Dailymotion. All rights reserved.
 //
 
+#ifdef SD_WEBP
 #import <UIKit/UIKit.h>
 
 @interface UIImage (WebP)
@@ -13,3 +14,4 @@
 + (UIImage *)sd_imageWithWebPData:(NSData *)data;
 
 @end
+#endif

@@ -6,6 +6,7 @@
 //  Copyright (c) 2013 Dailymotion. All rights reserved.
 //
 
+#ifdef SD_WEBP
 #import "UIImage+WebP.h"
 #import "webp/decode.h"
 
@@ -60,3 +61,4 @@ static void FreeImageData(void *info, const void *data, size_t size)
 }
 
 @end
+#endif