"half-screen" -> "right-half-screen".

(I don't know why this was needed, but calling it "half-screen" looks
like it's asking for future trouble.)

collects/slideshow/cmdline.rkt

@@ -44,7 +44,7 @@
     (define print-target #f)
     (define smoothing? #t)
     (define screen-number 0)
-    (define half-screen? #f)
+    (define right-half-screen? #f)
     
     (define init-page 0)
 
@@ -122,8 +122,8 @@
          (set! use-prefetch-in-preview? #t))
         (("--keep-titlebar") "give the slide window a title bar and resize border"
          (set! keep-titlebar? #t))
-        (("--half-screen") "display slides on right half of the screen"
-         (set! half-screen? #t)
+        (("--right-half-screen") "display slides on right half of the screen"
+         (set! right-half-screen? #t)
          (set! keep-titlebar? #t)
          (set! actual-screen-w (/ actual-screen-w 2)))
         (("--comment") "display commentary in window"

collects/slideshow/sig.rkt

@@ -99,7 +99,7 @@
      trust-me?
      quad-view?
      keep-titlebar?
-     half-screen? 
+     right-half-screen? 
      two-frames?
      use-prefetch?
      use-prefetch-in-preview?

collects/slideshow/viewer.rkt

@@ -414,7 +414,7 @@
 	    (values 0 0)
 	    (get-display-left-top-inset #:monitor config:screen-number)))
 
-      (when config:half-screen?
+      (when config:right-half-screen?
         (set! screen-left-inset (- screen-left-inset config:actual-screen-w)))
 
       (define fullscreen?