Add pillow 2.4.0 support

Pillow 2.4.0 added support for JPEG2000 using OpenJPEG 2.0. Because
Pillow calls the format JPEG2000 instead of JP2, we need to rename it to
enable the optimized code path. Should still be backwards compatible.

src/img2pdf.py

@@ -133,7 +133,7 @@ class pdfdoc(object):
         # either embed the whole jpeg or deflate the bitmap representation
         if imgformat is "JPEG":
             ofilter = [ "/DCTDecode" ]
-        elif imgformat is "JP2":
+        elif imgformat is "JPEG2000":
             ofilter = [ "/JPXDecode" ]
             self.version = 5 # jpeg2000 needs pdf 1.5
         else:
@@ -218,7 +218,7 @@ def convert(images, dpi, title=None, author=None, creator=None, producer=None,
                 exit(1)
             # image is jpeg2000
             width, height, ics = parsejp2(rawdata)
-            imgformat = "JP2"
+            imgformat = "JPEG2000"
 
             if dpi:
                 ndpi = dpi, dpi
@@ -256,7 +256,7 @@ def convert(images, dpi, title=None, author=None, creator=None, producer=None,
 
         # depending on the input format, determine whether to pass the raw
         # image or the zlib compressed color information
-        if imgformat is "JPEG" or imgformat is "JP2":
+        if imgformat is "JPEG" or imgformat is "JPEG2000":
             if color == '1':
                 error_out("jpeg can't be monochrome")
                 exit(1)