build failure

[Graham Percival]

Please don't do this.  Starting from doc-clean, clean, distclean, and
./autogen, I get:

Processing `/main/src/lilypond/ly/generate-documentation.ly'
Parsing...
[/main/src/lilypond/ly/init.ly
 [/main/src/lilypond/ly/declarations-init.ly
  [/main/src/lilypond/ly/markup-init.ly]
  [/main/src/lilypond/ly/music-functions-init.ly]
  [/main/src/lilypond/ly/toc-init.ly]
  [/main/src/lilypond/ly/nederlands.ly]
  [/main/src/lilypond/ly/drumpitch-init.ly]
  [/main/src/lilypond/ly/chord-modifiers-init.ly]
  [/main/src/lilypond/ly/script-init.ly]
  [/main/src/lilypond/ly/scale-definitions-init.ly]
  [/main/src/lilypond/ly/grace-init.ly]
  [/main/src/lilypond/ly/midi-init.ly
   [/main/src/lilypond/ly/performer-init.ly]]
  [/main/src/lilypond/ly/paper-defaults-init.ly
   [/main/src/lilypond/ly/titling-init.ly]]
  [/main/src/lilypond/ly/engraver-init.lyBacktrace:
In unknown file:
   ?:  0* [lilypond-main ("/main/src/lilypond/ly/generate-documentation")]
In /main/src/lilypond/out/share/lilypond/current/scm/lily.scm:
 656:  1* (let* ((failed #)) (if (ly:get-option #) (begin #)) ...)
 656:  2* [lilypond-all ("/main/src/lilypond/ly/generate-documentation")]
 670:  3  (let* ((failed #) (separate-logs #) (ping-log #) ...) (gc) ...)
 681:  4* [for-each #<procedure #f #> #]
In unknown file:
   ?:  5* [#<procedure #f (x)> "/main/src/lilypond/ly/generate-documentation"]
In /main/src/lilypond/out/share/lilypond/current/scm/lily.scm:
 683:  6* (let* (# # #) (if separate-logs #) (if ping-log #) ...)
 694:  7* [lilypond-file #<procedure #f #> ...]
 721:  8  [catch ly-file-failed #<procedure #f ()> #<procedure #f (x . args)>]
In unknown file:
   ?:  9* [#<procedure #f ()>]
In /main/src/lilypond/out/share/lilypond/current/scm/lily.scm:
 722: 10* [ly:parse-file "/main/src/lilypond/ly/generate-documentation"]

/main/src/lilypond/out/share/lilypond/current/scm/lily.scm:722:21: In
procedure ly:parse-file in expression (ly:parse-file file-name):
/main/src/lilypond/out/share/lilypond/current/scm/lily.scm:722:21:
Unbound variable: slur::draw-tab-slur
make[1]: *** [out/internals.texi] Error 1
rm out/contributor.texi out/general.texi
make[1]: Leaving directory `/main/src/lilypond/Documentation'
make: *** [all] Error 2