CORE: optimize time formatting, fix typo and wrong comment (#371)

'apply' is usually less effective as a direct call. For frequently called code this counts. Therefore we write better dispatch on tz0 with a test - see #371 for details.

Author: 0-8-15

modules/ln_core/time.scm

@@ -554,7 +554,7 @@ end-of-c-declare
 
 (define (time-utc->time-monotonic! time-in)
   (if (not (eq? (srfi19:time-type time-in) time-utc))
-      (tm:time-error 'time-utc->time-montonic! 'incompatible-time-types time-in))
+      (tm:time-error 'time-utc->time-monotonic! 'incompatible-time-types time-in))
   (let ((ntime (tm:time-utc->time-tai! time-in time-in
 				       'time-utc->time-monotonic!)))
     (srfi19:time-type-set! ntime time-monotonic)
@@ -1514,9 +1514,10 @@ end-of-c-declare
         )
     utc2))
 
-;; can't do optimization here as tz0 is needed later
 (define (string->seconds str fmt . tz0)
-  (apply string->seconds~ (append (list str (ln:tildify fmt)) tz0)))
+  (if (pair? tz0)
+      (string->seconds~ str (ln:tildify fmt) (car tz0))
+      (string->seconds~ str (ln:tildify fmt))))
 
 (define (seconds->string~ sec0 fmt tz)
   (let* ((sec (+ sec0 (* tz 3600.)))