ENH: allow space char in fileName is now configurable (#1008)

- having whitespace in fileName can be somewhat fragile since it means
  that the fileName components do not necessarily correspond to a
  'Foam::word'. But in many cases it will work provided that spaces
  are not present in the final portion of the simulation directory
  itself.

    InfoSwitches
    {
        // Allow space character in fileName (use with caution)
        allowSpaceInFileName    0;
    }

- now use doClean=true as default for fileName::validate(). Was false.

  Unlike fileName::clean() this requires no internal string rewrite
  since the characters are being copied.  Also handle any path
  separator transformations (ie, backslash => forward slash) at the
  same time. This makes it resemble the std::filesystem a bit more.

applications/test/fileNameOS/Make/files

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

applications/test/fileNameOS/Make/options

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

applications/test/fileNameOS/Test-fileNameOS.C

@@ -0,0 +1,106 @@
+/*---------------------------------------------------------------------------*\
+  =========                 |
+  \\      /  F ield         | OpenFOAM: The Open Source CFD Toolbox
+   \\    /   O peration     |
+    \\  /    A nd           | Copyright (C) 2019 OpenCFD Ltd.
+     \\/     M anipulation  |
+-------------------------------------------------------------------------------
+License
+    This file is part of OpenFOAM.
+
+    OpenFOAM is free software: you can redistribute it and/or modify it
+    under the terms of the GNU General Public License as published by
+    the Free Software Foundation, either version 3 of the License, or
+    (at your option) any later version.
+
+    OpenFOAM is distributed in the hope that it will be useful, but WITHOUT
+    ANY WARRANTY; without even the implied warranty of MERCHANTABILITY or
+    FITNESS FOR A PARTICULAR PURPOSE.  See the GNU General Public License
+    for more details.
+
+    You should have received a copy of the GNU General Public License
+    along with OpenFOAM.  If not, see <http://www.gnu.org/licenses/>.
+
+Application
+    Test-fileNameOS
+
+Description
+    Test fileName behaviour, potential OS capabilities etc.
+
+    In the distant future could possibly replace parts with C++ filesystem
+
+\*---------------------------------------------------------------------------*/
+
+#include "argList.H"
+#include "fileName.H"
+#include "OSspecific.H"
+#include "Switch.H"
+
+#include <csignal>
+#include <cstdlib>
+#include <iostream>
+
+
+using namespace Foam;
+
+// * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * //
+
+void testDirname(const std::string& rawInput)
+{
+    fileName input(fileName::validate(rawInput));
+
+    Info<< nl
+        << "input:   " << rawInput << nl
+        << "fileName:" << input << nl
+        << "   path:" << input.path()
+        << "   name:\"" << input.name() << '"'
+        << "   ext:\"" << input.ext()  << '"'
+        << "   components: " << flatOutput(input.components()) << nl;
+
+    if (rawInput.size() != input.size())
+    {
+        Info<< "   This would be Fatal with debug > 1" << nl;
+    }
+}
+
+
+// * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * //
+// Main program:
+
+int main(int argc, char *argv[])
+{
+    argList::noParallel();
+    argList::addBoolOption("no-space", "allowSpaceInFileName = false");
+    argList::addBoolOption("with-space", "set allowSpaceInFileName = true");
+
+    #include "setRootCase.H"
+
+    if (args.found("with-space"))
+    {
+        fileName::allowSpaceInFileName = true;
+    }
+
+    if (args.found("no-space"))
+    {
+        fileName::allowSpaceInFileName = false;
+
+    }
+
+
+    Info<<"fileName with spaces? : "
+        << Switch(bool(fileName::allowSpaceInFileName)) << nl << nl;
+
+
+    {
+        testDirname("/abc");
+        testDirname("/abc/with space/name");
+        testDirname("/abc/with space/more space");
+    }
+
+
+    Info<< "\nEnd\n" << endl;
+    return 0;
+}
+
+
+// ************************************************************************* //