BUG: still require IStringStream for argList (closes #672)

- regression introduced by part of commit 2787a866.

  Specifically the way that scalarRanges is written, it parses through
  until it hits invalid input. This works fine with an IStringStream,
  but the ITstream is pickier and reports this as being an error.

  So revert to IStringStream and be less picky about argList parsing.
  in the longer-term, should fix scalarRanges instead.

src/OpenFOAM/global/argList/argList.H

@@ -102,7 +102,7 @@ SourceFiles
 #include "fileName.H"
 #include "parRun.H"
 #include "OSspecific.H"
-#include "ITstream.H"
+#include "StringStream.H"
 #include <utility>
 
 // * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * //
@@ -308,8 +308,8 @@ public:
             //- Return how many of the specified options were used
             label optionCount(std::initializer_list<word> optionNames) const;
 
-            //- Return an input token stream for the named option
-            inline ITstream optionLookup(const word& optionName) const;
+            //- Return an input stream for the named option
+            inline IStringStream optionLookup(const word& optionName) const;
 
             //- Read a value from the named option
             template<class T>

src/OpenFOAM/global/argList/argListI.H

@@ -105,12 +105,12 @@ inline bool Foam::argList::optionFound(const word& optionName) const
 }
 
 
-inline Foam::ITstream Foam::argList::optionLookup
+inline Foam::IStringStream Foam::argList::optionLookup
 (
     const word& optionName
 ) const
 {
-    return ITstream(optionName, options_[optionName]);
+    return IStringStream(options_[optionName]);
 }