Python 3 fixes to gen-os2-unicode-ranges.py (#1521)

In Python 3, __reload()__ was moved and __sys.setdefaultencoding()__ because the default is already utf-8.  Also __Error()__ is an _undefined name_ and __Exception()__ creates a generic exception.

src/gen-os2-unicode-ranges.py

@@ -10,8 +10,11 @@ import io
 import re
 import sys
 
-reload(sys)
-sys.setdefaultencoding('utf-8')
+try:
+  reload(sys)
+  sys.setdefaultencoding('utf-8')
+except NameError:
+  pass  # Python 3
 
 print ("""static OS2Range _hb_os2_unicode_ranges[] =
 {""")
@@ -32,12 +35,12 @@ with io.open(input_file, mode="r", encoding="utf-8") as f:
       current_bit = fields[0]
       fields = fields[1:]
     elif len(fields) > 3:
-      raise Error("bad input :(.")
+      raise Exception("bad input :(.")
 
     name = fields[0]
     ranges = re.split("-", fields[1])
     if len(ranges) != 2:
-      raise Error("bad input :(.")
+      raise Exception("bad input :(.")
 
     v = tuple((int(ranges[0], 16), int(ranges[1], 16), int(current_bit), name))
     all_ranges.append(v)