* evalext.c, evalext.h: New files. Contain non-R5RS things

* evalext.c, evalext.h: New files.  Contain non-R5RS things
having to do with evaluation.
* evalext.c (serial-map): New procedure: Version of `map' which
guarantees that the procedure is applied to the lists in serial
order.
(sequence->list): New syntax: Version of `begin' which returns a
list of the results of the body forms instead of the result of the
last body form.
(scm_definedp, scm_m_undefine): Moved from eval.c
* evalext.h (scm_m_sequence_to_list): Added declaration.
* Makefile.am: Added evalext.c, evalext.h, macros.c, macros.h.