ENH: no string quotes when using OSHA1stream (#1301)

- previously would have different SHA1 depending on whether the
  string was a C-string, a C++-string or if the SHA1 was calculated
  directly or via the OSHA1stream.

    - SHA1("string")
    - OSHA1stream << "string";
    - OSHA1stream << string("string");

  By avoiding string quoting on output, they now all deliver the same
  result. This also means that the following will no longer change the SHA1
  content, since it does not add anything:

    osha<< string() << string() << string() << string();

  This would have previously add a pair of double quotes each time!