Automake cleanups.

Automake cleanups.

- Replace INCLUDES with AM_CPPFLAGS
  (INCLUDES has been replaced by AM_CPPFLAGS and is deprecated in
  modern automakes for several years)
- Require autoconf-2.61 and automake-1.10
  (already required by autogen.sh)
- update mkinstalldirs with the version from automake-1.10
  (The version in rpm is ancient and known to be bugged)

Patch from Ralf Corsepius