EclOutput: Add Stream Flushing Operation

Calls '.flush()' on the contained 'ofstream' object.  Needed as a
means of ensuring that bits in the internal buffers of the I/O
system are promptly output to permanent storage.  This, in turn, is
needed in upcoming work on the summary writing feature.

opm/io/eclipse/EclOutput.hpp

@@ -72,6 +72,7 @@ public:
     }
 
     void message(const std::string& msg);
+    void flushStream();
 
     friend class OutputStream::Restart;
     friend class OutputStream::SummarySpecification;

src/opm/io/eclipse/EclOutput.cpp

@@ -86,6 +86,10 @@ void EclOutput::message(const std::string& msg)
     this->write(msg, std::vector<char>{});
 }
 
+void EclOutput::flushStream()
+{
+    this->ofileH.flush();
+}
 
 void EclOutput::writeBinaryHeader(const std::string&arrName, int size, eclArrType arrType)
 {

src/opm/io/eclipse/OutputStream.cpp

@@ -744,8 +744,7 @@ void Opm::EclIO::OutputStream::SummarySpecification::rewindStream()
 
 void Opm::EclIO::OutputStream::SummarySpecification::flushStream()
 {
-    // Benefits from EclOutput friendship
-    this->stream().ofileH.flush();
+    this->stream().flushStream();
 }
 
 Opm::EclIO::EclOutput&