Support --disable-* switches to disable features.

For example, --disable-jpeg unconditionally disables both checks jpeg
support and checks for libjpeg.

setup.py

@@ -94,6 +94,32 @@ LCMS_ROOT = None
 
 class pil_build_ext(build_ext):
 
+    class feature:
+        zlib = jpeg = tiff = freetype = tcl = tk = lcms = webp = None
+
+        def __iter__(self):
+            for x in dir(self):
+                if x[1] != '_':
+                    yield x
+
+    feature = feature()
+
+    user_options = build_ext.user_options + [
+        ('disable-%s' % x, None, 'Disable support for %s' % x)
+        for x in feature
+    ]
+
+    def initialize_options(self):
+        build_ext.initialize_options(self)
+        for x in self.feature:
+            setattr(self, 'disable_%s' % x, None)
+
+    def finalize_options(self):
+        build_ext.finalize_options(self)
+        for x in self.feature:
+            if getattr(self, 'disable_%s' % x):
+                setattr(self.feature, x, False)
+
     def build_extensions(self):
 
         global TCL_ROOT
@@ -223,16 +249,16 @@ class pil_build_ext(build_ext):
         #
         # look for available libraries
 
-        class feature:
+        feature = self.feature
-            zlib = jpeg = tiff = freetype = tcl = tk = lcms = webp = None
-        feature = feature()
 
+        if feature.zlib is None:
             if _find_include_file(self, "zlib.h"):
                 if _find_library_file(self, "z"):
                     feature.zlib = "z"
                 elif sys.platform == "win32" and _find_library_file(self, "zlib"):
                     feature.zlib = "zlib"  # alternative name
 
+        if feature.jpeg is None:
             if _find_include_file(self, "jpeglib.h"):
                 if _find_library_file(self, "jpeg"):
                     feature.jpeg = "jpeg"
@@ -241,6 +267,7 @@ class pil_build_ext(build_ext):
                         _find_library_file(self, "libjpeg")):
                     feature.jpeg = "libjpeg"  # alternative name
 
+        if feature.tiff is None:
             if _find_library_file(self, "tiff"):
                 feature.tiff = "tiff"
             if sys.platform == "win32" and _find_library_file(self, "libtiff"):
@@ -248,6 +275,7 @@ class pil_build_ext(build_ext):
             if sys.platform == "darwin" and _find_library_file(self, "libtiff"):
                 feature.tiff = "libtiff"
 
+        if feature.freetype is None:
             if _find_library_file(self, "freetype"):
                 # look for freetype2 include files
                 freetype_version = 0
@@ -269,6 +297,7 @@ class pil_build_ext(build_ext):
                     if dir:
                         _add_directory(self.compiler.include_dirs, dir, 0)
 
+        if feature.lcms is None:
             if _find_include_file(self, "lcms.h"):
                 if _find_library_file(self, "lcms"):
                     feature.lcms = "lcms"
@@ -276,15 +305,18 @@ class pil_build_ext(build_ext):
         if _tkinter and _find_include_file(self, "tk.h"):
             # the library names may vary somewhat (e.g. tcl84 or tcl8.4)
             version = TCL_VERSION[0] + TCL_VERSION[2]
+            if feature.tcl is None:
                 if _find_library_file(self, "tcl" + version):
                     feature.tcl = "tcl" + version
                 elif _find_library_file(self, "tcl" + TCL_VERSION):
                     feature.tcl = "tcl" + TCL_VERSION
+            if feature.tk is None:
                 if _find_library_file(self, "tk" + version):
                     feature.tk = "tk" + version
                 elif _find_library_file(self, "tk" + TCL_VERSION):
                     feature.tk = "tk" + TCL_VERSION
 
+        if feature.webp is None:
             if (_find_include_file(self, "webp/encode.h") and
                     _find_include_file(self, "webp/decode.h")):
                 if _find_library_file(self, "webp"): # in googles precompiled zip it is call "libwebp"