Have presentations request their own full-screen clears

This will let custom ship spins use Presentations to
display data over themselves without wiping out the
underlyin image.

git-svn-id: svn://svn.code.sf.net/p/sc2/code/trunk@2845 8092fc87-c524-0410-9efc-e669fe64eaf9

sc2/content/slides/ending/ending.txt

@@ -2,11 +2,16 @@
 
 #(**** This script is a wrapper for 3 sequences ****)
 
+#(Clear entire screen first; set size...)
+DIMS 320 240
+
+#(... and clear)
+CLS
+
 #(Set sequence dimensions; param1=width; param2=height)
 DIMS 320 200
 #(Everything is drawn within the clipping rect defined by DIMS, from 0, 0)
 
-
 #(Sequence 1 -- position the bomb)
 CALL slides/ending/victory1.txt
 

sc2/content/slides/intro/intro.txt

@@ -5,6 +5,12 @@
 #( you MUST change timing of a subtitle, make sure this change is    )
 #( balanced off by another subtitle within the same slide!           )
 
+#(Clear entire screen first; set size...)
+DIMS 320 240
+
+#(... and clear)
+CLS
+
 #(Set sequence dimensions; param1=width; param2=height)
 DIMS 320 200
 #(Everything is drawn within the clipping rect defined by DIMS, from 0, 0)