py3: make doc/docchecker use print_function

doc/docchecker

@@ -1,66 +1,66
 #!/usr/bin/env python
 #
 # docchecker - look for problematic markup
 #
 # Copyright 2016 timeless <[e-mail]> and others
 #
 # This software may be used and distributed according to the terms of the
 # GNU General Public License version 2 or any later version.
 
-from __future__ import absolute_import
+from __future__ import absolute_import, print_function
 
 import re
 import sys
 
 leadingline = re.compile(r'(^\s*)(\S.*)$')
 
 checks = [
   (r""":hg:`[^`]*'[^`]*`""",
     """warning: please avoid nesting ' in :hg:`...`"""),
   (r'\w:hg:`',
     'warning: please have a space before :hg:'),
   (r"""(?:[^a-z][^'.])hg ([^,;"`]*'(?!hg)){2}""",
     '''warning: please use " instead of ' for hg ... "..."'''),
 ]
 
 def check(line):
     messages = []
     for match, msg in checks:
         if re.search(match, line):
             messages.append(msg)
     if messages:
         print(line)
         for msg in messages:
             print(msg)
 
 def work(file):
     (llead, lline) = ('', '')
 
     for line in file:
         # this section unwraps lines
         match = leadingline.match(line)
         if not match:
             check(lline)
             (llead, lline) = ('', '')
             continue
 
         lead, line = match.group(1), match.group(2)
         if (lead == llead):
             if (lline != ''):
                 lline += ' ' + line
             else:
                 lline = line
         else:
             check(lline)
             (llead, lline) = (lead, line)
     check(lline)
 
 def main():
     for f in sys.argv[1:]:
         try:
             with open(f) as file:
                 work(file)
         except BaseException as e:
             print("failed to process %s: %s" % (f, e))
 
 main()