*/Makefile.am: Replace INCLUDES with AM_CPPFLAGS

*/Makefile.am: Replace INCLUDES with AM_CPPFLAGS

Catch up with Automake's [1], which was part of v1.6b, cut 2002-07-28
[2].  Avoids:

  $ autoreconf -v -f --install
  ...
  libmisc/Makefile.am:4: warning: 'INCLUDES' is the old name for 'AM_CPPFLAGS' (or '*_CPPFLAGS')
  ...
  src/Makefile.am:10: warning: 'INCLUDES' is the old name for 'AM_CPPFLAGS' (or '*_CPPFLAGS')
  ...

Consolidating with the earlier AM_CPPFLAGS avoids:

  $ autoreconf -v -f --install
  src/Makefile.am:72: warning: AM_CPPFLAGS multiply defined in condition TRUE ...
  src/Makefile.am:10: ... 'AM_CPPFLAGS' previously defined here
  autoreconf-2.69: Leaving directory `.'

[1]: http://git.savannah.gnu.org/cgit/automake.git/commit/?id=1415d22f6203206bc393fc4ea233123ba579222d
     Summary: automake.in (generate_makefile): Suggest using AM_CPPFLAGS instead of INCLUDES
     Date: 2002-07-09
[2]: http://git.savannah.gnu.org/cgit/automake.git/tag/?id=Release-1-6b