ENH: make treatment of stream allocators more uniform (issue #532)

- use allocator class to wrap the stream pointers instead of passing
  them into ISstream, OSstream and using a dynamic cast to delete
  then. This is especially important if we will have a bidirectional
  stream (can't delete twice!).

STYLE:

- file stream constructors with std::string (C++11)

- for rewind, explicit about in|out direction. This is not currently
  important, but avoids surprises with any future bidirectional access.

- combined string streams in StringStream.H header.
  Similar to <sstream> include that has both input and output string
  streams.

src/sampling/sampledSurface/readers/ensight/ensightSurfaceReader.H

@@ -37,6 +37,7 @@ SourceFiles
 
 #include "surfaceReader.H"
 #include "ensightReadFile.H"
+#include "StringStream.H"
 #include "Tuple2.H"
 
 // * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * //

src/sampling/sampledSurface/writers/ensight/ensightSurfaceWriterTemplates.C

@@ -30,7 +30,7 @@ License
 #include "ensightPartFaces.H"
 #include "ensightSerialOutput.H"
 #include "ensightPTraits.H"
-#include "OStringStream.H"
+#include "StringStream.H"
 
 // * * * * * * * * * * * * * Private Member Functions  * * * * * * * * * * * //