Options with multiple values get split to send to subprocess #204
  Add this suggestion to a batch that can be applied as a single commit.
  This suggestion is invalid because no changes were made to the code.
  Suggestions cannot be applied while the pull request is closed.
  Suggestions cannot be applied while viewing a subset of changes.
  Only one suggestion per line can be applied in a batch.
  Add this suggestion to a batch that can be applied as a single commit.
  Applying suggestions on deleted lines is not supported.
  You must change the existing code in this line in order to create a valid suggestion.
  Outdated suggestions cannot be applied.
  This suggestion has been applied or marked resolved.
  Suggestions cannot be applied from pending reviews.
  Suggestions cannot be applied on multi-line comments.
  Suggestions cannot be applied while the pull request is queued to merge.
  Suggestion cannot be applied right now. Please check back later.
  
    
  
    
When an option like --custom-header Authorization my-token is received this must be broken in to 3 strings to be given to subprocess.Popen
With the previous code where "Authorization my-token" was one string, Popen does not correctly pass both arguments with --custom-header. Consequently wkhtmltopdf ignores any --custom-header instruction sent to it from django-wkhtml. The problem can be seen by running these commands:
If you change the above command to be
cmd = ['curl', '--dump-header', 'output', 'https://api.github.com']
then the call works and makes a file called "output" containing header information.