Only call tqdm.write (which inserts a newline) if
DummyTqdmFile.write is itself called with a string containing a
newline; otherwise buffer the rest of the string.

See changes in test_tqdm.py for the patterns this allows.

• I have marked all applicable categories:
  • exception-raising fix
  • visual output fix
  • documentation modification
  • new feature
• If applicable, I have mentioned the relevant/related issue(s)

Less important but also useful:

• I have visited the source website, and in particular
  read the known issues
• I have searched through the issue tracker for duplicates
• I have mentioned version numbers, operating system and
  environment, where applicable:

  import tqdm, sys
  print(tqdm.__version__, sys.version, sys.platform)