Merge branch 'yacc-work' into yl-work-for-master

Merge branch 'yacc-work' into yl-work-for-master

* yacc-work: (37 commits)
  fixup: list of yacc/lex tests was botched
  tests: work around bug#7884 in many yacc/lex tests
  yacc/lex tests: remove an unneeded workaround for bug#8485
  yacc/lex tests: avoid too much failures with FreeBSD make
  yacc-dist-nobuild.test: add reference to bug#7884
  yacc tests: fix bug in 'yacc-cxx.test'
  lex tests: fix spurious link errors on Solaris
  lex: "make clean" removes .c files from non-distributed .l
  lex tests: make test on Lex dependency tracking more "semantic"
  lex tests: remove erroneous check about ylwrap distribution
  yacc tests: "make clean" removes C++ files from non-distributed .y
  tests: add a workaround for automake bug#8485
  tests: add a couple of inter-tests reference
  lex tests: require just `lex' instead of `flex'
  fix typo in ChangeLog (2011-05-04)
  tests defs: use `skip_' for skipping yacc/lex related tests
  lex/yacc tests: remove redundant $distdir definition
  coverage: test lex-generated "#line" directives postprocessing
  tests: minor improvements to a couple of yacc tests
  tests: fix spurious failure in test 'yacc-d-cxx.test'
  ...

+ Extra non-trivial edits:

* tests/defs.in: Delete; the differences from maint has been
merged into 'tests/defs' and 'tests/defs-static.in'.
* tests/defs (yacc, lex): Use 'skip_all_', not 'skip_', to
skip the whole test case if yacc (resp. lex) is missing.
(bison): New, set up the environment so that 'bison -y' will
be used as the yacc program.
(useless_vpath_rebuild, yl_distcheck): Moved in from
'tests/defs.in'.
* tests/defs-static.in ($YACC, $LEX): Default to the values
determined at configure time, and allow them to be overridden
by the more namespace-safe variables '$AM_TESTSUITE_YACC' and
'$AM_TESTSUITE_LEX' respectively.
* tests/Makefile.am (do_subst): Also substitute '@YACC@' and
'@LEX@'.
* Several tests: Fix requirements declarations, by preferring
'lex' and 'yacc' over 'flex' and 'bison' whenever possible.