VS: Add CSharp project uuid and file extension

This is in preparation for adding CSharp language support to the VS
generator.

Source/cmGlobalVisualStudio71Generator.cxx

@@ -159,6 +159,10 @@ void cmGlobalVisualStudio71Generator::WriteProject(std::ostream& fout,
     ext = ".vfproj";
     project = "Project(\"{6989167D-11E4-40FE-8C1A-2192A86A7E90}\") = \"";
   }
+  if (this->TargetIsCSharpOnly(t)) {
+    ext = ".csproj";
+    project = "Project(\"{FAE04EC0-301F-11D3-BF4B-00C04F79EFBC}\") = \"";
+  }
   const char* targetExt = t->GetProperty("GENERATOR_FILE_NAME_EXT");
   if (targetExt) {
     ext = targetExt;

Source/cmGlobalVisualStudioGenerator.cxx

@@ -734,6 +734,27 @@ bool cmGlobalVisualStudioGenerator::TargetIsFortranOnly(
   return false;
 }
 
+bool cmGlobalVisualStudioGenerator::TargetIsCSharpOnly(
+  cmGeneratorTarget const* gt)
+{
+  // check to see if this is a C# build
+  std::set<std::string> languages;
+  {
+    // Issue diagnostic if the source files depend on the config.
+    std::vector<cmSourceFile*> sources;
+    if (!gt->GetConfigCommonSourceFiles(sources)) {
+      return false;
+    }
+  }
+  gt->GetLanguages(languages, "");
+  if (languages.size() == 1) {
+    if (*languages.begin() == "CSharp") {
+      return true;
+    }
+  }
+  return false;
+}
+
 bool cmGlobalVisualStudioGenerator::TargetCompare::operator()(
   cmGeneratorTarget const* l, cmGeneratorTarget const* r) const
 {

Source/cmGlobalVisualStudioGenerator.h

@@ -69,6 +69,9 @@ public:
   // return true if target is fortran only
   bool TargetIsFortranOnly(const cmGeneratorTarget* gt);
 
+  // return true if target is C# only
+  static bool TargetIsCSharpOnly(cmGeneratorTarget const* gt);
+
   /** Get the top-level registry key for this VS version.  */
   std::string GetRegistryBase();