BUG: Error when install dir cannot be created

This teaches the undocumented file(INSTALL) command to report an error
when it cannot create the destination directory.

Source/cmFileCommand.cxx

@@ -1192,6 +1192,10 @@ bool cmFileInstaller::InstallDirectory(const char* source,
   // Make sure the destination directory exists.
   if(!cmSystemTools::MakeDirectory(destination))
     {
+    cmOStringStream e;
+    e << "INSTALL cannot make directory \"" << destination << "\": "
+      << cmSystemTools::GetLastSystemError();
+    this->FileCommand->SetError(e.str().c_str());
     return false;
     }