Improve octal-escape output in bool vectors and strings

Improve octal-escape output in bool vectors and strings

* src/print.c (octalout): New function.
(print_vectorlike): When printing bool vectors, use
octal escapes for control characters when
print-escape-control-characters is non-nil, so that
the printed representation avoids encoding issues.
Rename locals to avoid byte-vs-char confusion.
(print_object): Don't output unnecessary zeros when
printing octal escapes.  Simplify by using octalout.