* gc.h (SCM_[SET_]CELL_{WORD,OBJECT}, SCM_VALIDATE_CELL): brought

* gc.h (SCM_[SET_]CELL_{WORD,OBJECT}, SCM_VALIDATE_CELL): brought
the yucky, ugly and nasty conditional compilation back.  sorry,
but it was either that or requiring GAWK to build Guile.
removed the code that implemented the old GC scheme.

* init.c (scm_boot_guile_1): removed the code conditioned on
!GUILE_NEW_GC_SCHEME.

* __scm.h: (GUILE_NEW_GC_SCHEME): removed.

* gc.c (scm_protect_object, scm_unprotect_object): change the
implementation to more efficient (at least in the time complexity
sense).  the calls should now also be thread-safe -- I suspect
that people expect them to be.  (thanks to Han-Wen Nienhuys)
removed the code that implemented the old GC scheme.

* hashtab.c (scm_hash_fn_create_handle_x): add missing
SCM_REALLOW_INTS before return.