ENH: direct access to wrapped ifstream/ofstream with compression (#1805)

- previously hidden as Detail::[IO]FstreamAllocator, now exposed
  directly as [io]fstreamPointer, which allows reuse for
  std::ifstream, std::ofstream wrapping, without the additional
  ISstream, OSstream layers.

  These stream pointers have some characteristics similar to a
  unique_ptr.

- restrict direct gzstream usage to two files (fstreamPointers.C,
  gzstream.C) which improves localization and makes it simpler to
  enable/disable with the `HAVE_LIBZ` define.

  The HAVE_LIBZ define is currently simply hard-coded in the
  Make/options.

  If compiled WITHOUT libz support:
    - reading gz files : FatalError
    - writing gz files : emit warning and downgrade to uncompressed
    - warn if compression is specified in the case controlDict
      and downgrade to uncompressed

ENH: minor updates to gzstream interface for C++11

- support construct/open with std::string for the file names.

CONFIG: provisioning for have_libz detection as wmake/script

applications/test/fstreamPointer/Make/files

@@ -0,0 +1,3 @@
+Test-fstreamPointer.C
+
+EXE = $(FOAM_USER_APPBIN)/Test-fstreamPointer

applications/test/fstreamPointer/Make/options

@@ -0,0 +1,2 @@
+/* EXE_INC = */
+/* EXE_LIBS = */

applications/test/fstreamPointer/Test-fstreamPointer.C

@@ -0,0 +1,114 @@
+/*---------------------------------------------------------------------------*\
+  =========                 |
+  \\      /  F ield         | OpenFOAM: The Open Source CFD Toolbox
+   \\    /   O peration     |
+    \\  /    A nd           | www.openfoam.com
+     \\/     M anipulation  |
+-------------------------------------------------------------------------------
+    Copyright (C) 2020 OpenCFD Ltd.
+-------------------------------------------------------------------------------
+License
+    This file is part of OpenFOAM, distributed under GPL-3.0-or-later.
+
+Application
+    Test-fstreamPointer
+
+Description
+    Low-level fstream tests
+
+\*---------------------------------------------------------------------------*/
+
+#include "argList.H"
+#include "refPtr.H"
+#include "fstreamPointer.H"
+
+using namespace Foam;
+
+// * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * //
+//  Main program:
+
+int main(int argc, char *argv[])
+{
+    argList::noBanner();
+    argList::noParallel();
+
+    argList::addOption
+    (
+        "output",
+        "file",
+        "Output file name for cat"
+    );
+
+    argList::addArgument("file1");
+    argList::addArgument("...");
+    argList::addArgument("fileN");
+
+    argList::noMandatoryArgs();
+
+    #include "setRootCase.H"
+
+    if (args.size() <= 1)
+    {
+        InfoErr<< "\nNo input files specified .. stopping\n" << endl;
+        return 0;
+    }
+
+    refPtr<std::ostream> osRef;
+
+    fileName outputName;
+    if (args.readIfPresent("output", outputName))
+    {
+        InfoErr<< "output: " << outputName;
+
+        IOstreamOption::compressionType comp(IOstreamOption::UNCOMPRESSED);
+        if (outputName.hasExt("gz"))
+        {
+            comp = IOstreamOption::COMPRESSED;
+            outputName.removeExt();
+
+            InfoErr<< " [compress]";
+        }
+        InfoErr<< nl;
+
+        osRef.reset(ofstreamPointer(outputName, comp).release());
+    }
+    else
+    {
+        osRef.ref(std::cout);
+        InfoErr<< "output: stdout" << nl;
+    }
+    auto& os = osRef.ref();
+
+    for (label argi = 1; argi < args.size(); ++argi)
+    {
+        const fileName inputName(args[argi]);
+
+        InfoErr<< "input: " << inputName;
+
+        ifstreamPointer isPtr(inputName);
+
+        if (!isPtr.get() || !isPtr->good())
+        {
+            InfoErr<< " (not good)" << nl;
+            continue;
+        }
+        InfoErr<< nl;
+
+        auto& is = *isPtr;
+
+        // Loop getting single characters
+        // - not efficient, but that is not the test here anyhow
+
+        char c;
+        while (is.get(c))
+        {
+            os << c;
+        }
+    }
+
+    InfoErr<< "\nEnd\n" << endl;
+    return 0;
+}
+
+
+// ************************************************************************* //