title not centered

[James Bailey]

It seems that titles aren't centered on non-a4 size paper.  
Additionally, it appears that this is a regression that broke between  
2.13.11 and 2.13.12.

Consider the following input file:
\version "2.12.3"
\paper { #(set-paper-size "11x17") }
\header { title = \markup \center-column { "How Razorback Jumping  
Frogs Level Six Piqued Gymnasts" } }

\score {
   \new Staff {s1}
   \layout { }
}