py3: read in raw data files as binary

Not specifying the mode means it will be open in text mode which can
munge linebreaks on some platforms and yields the wrong type of string
on py3.

src/calibre/gui2/actions/edit_metadata.py

@@ -937,7 +937,7 @@ class EditMetadataAction(InterfaceAction):
                 if old != prefs['read_file_metadata']:
                     prefs['read_file_metadata'] = old
             if mi.cover and os.access(mi.cover, os.R_OK):
-                with open(mi.cover) as f:
+                with open(mi.cover, 'rb') as f:
                     cdata = f.read()
             elif mi.cover_data[1] is not None:
                 cdata = mi.cover_data[1]

src/calibre/gui2/metadata/single.py

@@ -461,7 +461,7 @@ class MetadataSingleDialogBase(QDialog):
             return
         cdata = None
         if mi.cover and os.access(mi.cover, os.R_OK):
-            with open(mi.cover) as f:
+            with open(mi.cover, 'rb') as f:
                 cdata = f.read()
         elif mi.cover_data[1] is not None:
             cdata = mi.cover_data[1]

src/calibre/utils/fonts/win_fonts.py

@@ -148,7 +148,7 @@ def load_winfonts():
 
 def test_ttf_reading():
     for arg in sys.argv[1:]:
-        with open(arg) as f:
+        with open(arg, 'rb') as f:
             raw = f.read()
         print(os.path.basename(arg))
         get_font_characteristics(raw)