doc update needed 2.11.x

[Stan Sanderson]

Documentation for LilyPond 2.11.17, Section 7.5.7, Other guitar issues-
guitar position/barring indication syntax has not been updated. The  
included snippet shows a dashed line with no bar numeral.

As included (works under 2.10, doesn't work under 2.11):
{
\clef "G_8"
b16 d16 g16 b16 e16
\textSpannerDown
\override TextSpanner #'edge-text = #'("XII " . "")
  g16\startTextSpan
  b16 e16 g16 e16 b16 g16\stopTextSpan
e16 b16 g16 d16
}

What works:

{
\clef "G_8"
b16 d16 g16 b16 e16
\textSpannerDown
\override TextSpanner #'bound-details #'left #'text = "XII "
  g16\startTextSpan
  b16 e16 g16 e16 b16 g16\stopTextSpan
e16 b16 g16 d16
}

If I missed previous discussion about this, please forgive.

Stan