* tags.h: Reduced the number of short instructions from 14 to 13.

	* tags.h: Reduced the number of short instructions from 14 to 13.
	The typecode of the former 14th short instruction is now used to
	represent long instructions.  Changed some comments to reflect
	this fact.

	(SCM_MAKISYM): ISYMs get a new tc7 code, namely the one that was
	previously used by SCM_IM_DEFINE.

	(SCM_IM_DEFINE): Turned into a long instruction.

	* eval.c (unmemocopy, SCM_CEVAL): Treat SCM_IM_DEFINE as a long
	instruction.

	* eval.c (SCM_CEVAL): Since characters and iflags have now a tc7
	code that is separate from all instructions, one level of dispatch
	for long instructions can be eliminated.

	* print.c (scm_isymnames): Removed some commented code.