* configure.in: big overhaul to shift us to have separate private,

* configure.in: big overhaul to shift us to have separate private,
config.h, and public, scmconfig.h, configuration headers.  Added a
fair amount of code to track down new required types: scm_t_uint8,
scm_t_uint16, scm_t_uint32, scm_t_int8, scm_t_int16, scm_t_int32,
and to detect optional types scm_t_uint64, scm_t_in64, long long,
unsigned long long, scm_t_ptrdiff, intptr_t, and uintptr_t.
(SCM_I_GSC_T_PTRDIFF): gen-scmconfig.h.in AC_SUBST var.
(SCM_I_GSC_NEEDS_INTTYPES_H): gen-scmconfig.h.in AC_SUBST var.
(SCM_I_GSC_NEEDS_STDINT_H): gen-scmconfig.h.in AC_SUBST var.
(SCM_I_GSC_T_UINT8): gen-scmconfig.h.in AC_SUBST var.
(SCM_I_GSC_T_UINT16): gen-scmconfig.h.in AC_SUBST var.
(SCM_I_GSC_T_UINT32): gen-scmconfig.h.in AC_SUBST var.
(SCM_I_GSC_T_UINT64): gen-scmconfig.h.in AC_SUBST var.
(SCM_I_GSC_T_INT8): gen-scmconfig.h.in AC_SUBST var.
(SCM_I_GSC_T_INT16): gen-scmconfig.h.in AC_SUBST var.
(SCM_I_GSC_T_INT32): gen-scmconfig.h.in AC_SUBST var.
(SCM_I_GSC_T_INT64): gen-scmconfig.h.in AC_SUBST var.
(USE_PTHREAD_THREADS): removed - handled by gen-scmconfig.c.
(USE_NULL_THREADS): removed - handled by gen-scmconfig.c.
(USE_COOP_THREADS): removed - handled by gen-scmconfig.c.
(SCM_I_GSC_USE_PTHREAD_THREADS): gen-scmconfig.h.in AC_SUBST var.
(SCM_I_GSC_USE_NULL_THREADS): gen-scmconfig.h.in AC_SUBST var.
(SCM_I_GSC_USE_COOP_THREADS): gen-scmconfig.h.in AC_SUBST var.
(STACK_GROWS_UP): removed - handled by gen-scmconfig.c.
(SCM_I_GSC_STACK_GROWS_UP): gen-scmconfig.h.in AC_SUBST var.
(GUILE_DEBUG_FREELIST): removed - handled by gen-scmconfig.c.
(SCM_I_GSC_GUILE_DEBUG_FREELIST): gen-scmconfig.h.in AC_SUBST var.
(GUILE_DEBUG): removed - handled by gen-scmconfig.c.
(SCM_I_GSC_GUILE_DEBUG): gen-scmconfig.h.in AC_SUBST var.
(SCM_ENABLE_DEPRECATED): removed - handled by gen-scmconfig.c.
(SCM_I_GSC_ENABLE_DEPRECATED): gen-scmconfig.h.in AC_SUBST var.
(HAVE_ARRAYS): removed - handled by gen-scmconfig.c.
(SCM_I_GSC_HAVE_ARRAYS): gen-scmconfig.h.in AC_SUBST var.
(SCM_ENABLE_ELISP): removed - handled by gen-scmconfig.c.
(SCM_I_GSC_ENABLE_ELISP): gen-scmconfig.h.in AC_SUBST var.
(SCM_I_GSC_C_INLINE): gen-scmconfig.h.in AC_SUBST var.
(DEBUG_EXTENSIONS): removed - handled by gen-scmconfig.c.
(READER_EXTENSIONS): removed - handled by gen-scmconfig.c.
(USE_THREADS): removed - handled by gen-scmconfig.c.
(GUILE_ISELECT): removed - handled by gen-scmconfig.c.
(DYNAMIC_LINKING): removed - handled by gen-scmconfig.c.