ENH: On VMS use _dir and _tmp, not .dir and .tmp

The VMS posix path emulation does not handle multiple '.' characters in
file names in all cases.  This avoids adding extra '.'s to file and
directory names for target directories and generated files.

Source/cmGeneratedFileStream.cxx

@@ -150,7 +150,11 @@ void cmGeneratedFileStreamBase::Open(const char* name)
 
   // Create the name of the temporary file.
   this->TempName = name;
+#if defined(__VMS)
+  this->TempName += "_tmp";
+#else
   this->TempName += ".tmp";
+#endif
 
   // Make sure the temporary file that will be used is not present.
   cmSystemTools::RemoveFile(this->TempName.c_str());