VS: Refactor handling of "header" sources in VS >= 10

Create a WriteHeaderSource method to handle writing of sources
classified by cmGeneratorTarget as header files.  This will be
useful to add special VS-specific handling for some headers.

Source/cmVisualStudio10TargetGenerator.cxx

@@ -997,6 +997,11 @@ WriteGroupSources(const char* name,
   this->WriteString("</ItemGroup>\n", 1);
 }
 
+void cmVisualStudio10TargetGenerator::WriteHeaderSource(cmSourceFile const* sf)
+{
+  this->WriteSource("ClInclude", sf);
+}
+
 void cmVisualStudio10TargetGenerator::WriteExtraSource(cmSourceFile const* sf)
 {
   this->WriteSource("None", sf);
@@ -1079,7 +1084,11 @@ void cmVisualStudio10TargetGenerator::WriteAllSources()
 
   std::vector<cmSourceFile const*> headerSources;
   this->GeneratorTarget->GetHeaderSources(headerSources, "");
-  this->WriteSources("ClInclude", headerSources);
+  for(std::vector<cmSourceFile const*>::const_iterator
+        si = headerSources.begin(); si != headerSources.end(); ++si)
+    {
+    this->WriteHeaderSource(*si);
+    }
   std::vector<cmSourceFile const*> idlSources;
   this->GeneratorTarget->GetIDLSources(idlSources, "");
   this->WriteSources("Midl", idlSources);

Source/cmVisualStudio10TargetGenerator.h

@@ -57,6 +57,7 @@ private:
   void WriteProjectConfigurations();
   void WriteProjectConfigurationValues();
   void WriteMSToolConfigurationValues(std::string const& config);
+  void WriteHeaderSource(cmSourceFile const* sf);
   void WriteExtraSource(cmSourceFile const* sf);
   void WriteSource(std::string const& tool, cmSourceFile const* sf,
                    const char* end = 0);