[clang-rename] make clang-rename.py vim integration python3 compatible

[JonasToth]

Summary

This patch makes the clang-rename.py script useable for vim with only python3
support. It uses the print-function and adjust the doc slightly to mention
the correct python3 command for the letter mapping in vim.

[JonasToth]

• remove double blank line

[hokein]

Thanks, LGTM.

[JonasToth]

• rebase

[JonasToth]

@hokein Do you think this should go into the 7.0 release?

tools/clang-rename/clang-rename.py

 '''
 Minimal clang-rename integration with Vim.
 
 Before installing make sure one of the following is satisfied:
 
 * clang-rename is in your PATH
 * `g:clang_rename_path` in ~/.vimrc points to valid clang-rename executable
 * `binary` in clang-rename.py points to valid to clang-rename executable
 
-To install, simply put this into your ~/.vimrc
+To install, simply put this into your ~/.vimrc for python2 support
 
     noremap <leader>cr :pyf <path-to>/clang-rename.py<cr>
 
+For python3 use the following command (note the change from :pyf to :py3f)
+
+    noremap <leader>cr :py3f <path-to>/clang-rename.py<cr>
+
 IMPORTANT NOTE: Before running the tool, make sure you saved the file.
 
 All you have to do now is to place a cursor on a variable/function/class which
 you would like to rename and press '<leader>cr'. You will be prompted for a new
 name if the cursor points to a valid symbol.
 '''
 
+from __future__ import print_function
 import vim
 import subprocess
 import sys
 
 def main():
     binary = 'clang-rename'
     if vim.eval('exists("g:clang_rename_path")') == "1":
         binary = vim.eval('g:clang_rename_path')
 
     # Get arguments for clang-rename binary.
     offset = int(vim.eval('line2byte(line("."))+col(".")')) - 2
     if offset < 0:
-        print >> sys.stderr, '''Couldn\'t determine cursor position.
-                                Is your file empty?'''
+        print('Couldn\'t determine cursor position. Is your file empty?',
+              file=sys.stderr)
         return
     filename = vim.current.buffer.name
 
     new_name_request_message = 'type new name:'
     new_name = vim.eval("input('{}\n')".format(new_name_request_message))
 
     # Call clang-rename.
     command = [binary,
                filename,
                '-i',
                '-offset', str(offset),
                '-new-name', str(new_name)]
     # FIXME: make it possible to run the tool on unsaved file.
     p = subprocess.Popen(command,
                          stdout=subprocess.PIPE,
                          stderr=subprocess.PIPE)
     stdout, stderr = p.communicate()
 
     if stderr:
-        print stderr
+        print(stderr)
 
     # Reload all buffers in Vim.
     vim.command("checktime")
 
 
 if __name__ == '__main__':
     main()