VS10: stop build on custom command error (#11533)

In VS9 and previous versions, :VCReportError is the goto label
to jump to after a failed custom command. It stops the build
before it tries to go any further.

In VS10, :VCEnd is the correct label to use.

Create a method in the VS generators to provide the correct
line of script to use for each version of Visual Studio.

For more internal details, search for VCEnd in the
C:\Program Files\MSBuild directory.

Source/cmLocalVisualStudioGenerator.h

@@ -30,6 +30,7 @@ class cmLocalVisualStudioGenerator : public cmLocalGenerator
 public:
   cmLocalVisualStudioGenerator();
   virtual ~cmLocalVisualStudioGenerator();
+
   /** Construct a script from the given list of command lines.  */
   std::string ConstructScript(const cmCustomCommandLines& commandLines,
                               const char* workingDirectory,
@@ -38,7 +39,13 @@ public:
                               bool escapeAllowMakeVars,
                               const char* newline = "\n");
 
+  /** Line of batch file text that skips to the end after
+    * a failed step in a sequence of custom commands.
+    */
+  std::string GetCheckForErrorLine();
+
 protected:
+  virtual std::string CheckForErrorLine();
 
   /** Construct a custom command to make exe import lib dir.  */
   cmsys::auto_ptr<cmCustomCommand>