Fix a memory leak in scm_read_line and a type cast bug in the ptob.

	Fix a memory leak in scm_read_line and a type cast bug in the ptob.
	* fports.c (scm_fgets): Use malloc/free rather than scm_must_malloc
 	and scm_must_free, since ultimately the	string returned will be copied
 	by scm_makfrom0str anyway.  Also, read any characters that may have
	been pushed onto the port with scm_ungetc.
	* ports.c (scm_generic_fgets): Same as for scm_fgets.
	* ioext.c (scm_read_line): Free string after Guilifying it.
	* ports.h (scm_ptobfuns): fgets method returns a char *, not a char.