Add support for Bison 3.0.

We still want to remain compatible with Bison 2.7 so instead of fixing
all the new errors reported by 3.0 we silence some warning.  We should
fix these for good once Bison 3.0 is more widespread.

* m4/bison.m4: New file. Test if bison support -Wno-empty-rule and
-Wno-deprecated.  Define BISON and BISON_EXTRA_FLAGS.
* configure.ac: Do not test for yacc, use the above test instead.
* src/dstarparse/Makefile.am, src/eltlparse/Makefile.am,
src/kripkeparse/Makefile.am, src/ltlparse/Makefile.am,
src/neverparse/Makefile.am, src/tgbaparse/Makefile.am: Use BISON
and BISON_EXTRA_FLAGS.
* src/ltlparse/ltlparse.yy: Fix or and remove useless %right/%nonassoc
settings.
* src/eltlparse/eltlparse.yy: Likewise, and remove "%pure-parser".

m4/bison.m4

@@ -0,0 +1,15 @@
+AC_DEFUN([adl_CHECK_BISON],
+[AC_ARG_VAR([BISON], [Bison parser generator])
+AC_CHECK_PROGS([BISON], [bison])
+if test -n "$BISON"; then
+   # Bison 3.0 has warning about issues that cannot be fixed in a
+   # compatible way with Bison 2.7.  Since we want to be compatible
+   # with both version AND use -Werror, disable those warnings.
+   # (Unfortunately -Wno-error=empty-rule,no-error=deprecated does not
+   # work: https://lists.gnu.org/archive/html/bug-bison/2013-09/index.html)
+   opt='-Wno-empty-rule -Wno-deprecated -Wno-precedence'
+   if AM_RUN_LOG([$BISON $opt --version]); then
+      BISON_EXTRA_FLAGS=$opt
+   fi
+fi
+AC_SUBST([BISON_EXTRA_FLAGS])])