build: ship the ASCII art figures

We don't ship the *.txt files that are used to build the info
file.
Reported by Colin Daley.

* doc/figs/example.txt: New.
* doc/local.mk (bison.info): Depend on the txt files.
And ship them.

THANKS

@@ -25,6 +25,7 @@ Bruce Lilly               blilly@erols.com
 Bruno Haible              bruno@clisp.org
 Charles-Henri de Boysson  de-boy_c@epita.fr
 Christian Burger          cburger@sunysb.edu
+Colin Daley               colin.daley@outlook.com
 Cris Bailiff              c.bailiff+bison@awayweb.com
 Cris van Pelt             cris@amf03054.office.wxs.nl
 Csaba Raduly              csaba_22@yahoo.co.uk

doc/figs/example.txt

@@ -0,0 +1,2 @@
+This file is a stub, not used by the documentation.  If you feel like
+contributing ASCII art for example.gv, please step forward!

doc/local.mk

@@ -24,6 +24,7 @@ doc_bison_TEXINFOS =                            \
 # Obfuscate with a variable.
 doc_bison = doc/bison
 $(doc_bison).dvi: $(FIGS_GV:.gv=.eps)
+$(doc_bison).info: $(FIGS_GV:.gv=.txt)
 $(doc_bison).pdf: $(FIGS_GV:.gv=.pdf)
 $(doc_bison).html: $(FIGS_GV:.gv=.png)
 
@@ -128,7 +129,7 @@ FIGS_GV =                                               \
   doc/figs/example.gv                                   \
   doc/figs/example-reduce.gv doc/figs/example-shift.gv
 EXTRA_DIST +=                                                   \
-  $(FIGS_GV)                                                    \
+  $(FIGS_GV) $(FIGS_GV:.gv=.txt)                                \
   $(FIGS_GV:.gv=.eps) $(FIGS_GV:.gv=.pdf) $(FIGS_GV:.gv=.png)
 SUFFIXES += .gv .eps .pdf .png