[py] minor, replace exit with sys.exit

src/gen-harfbuzzcc.py

@@ -5,7 +5,7 @@
 import os, sys, shutil
 
 if len (sys.argv) < 3:
-	exit (__doc__)
+	sys.exit (__doc__)
 
 OUTPUT = sys.argv[1]
 CURRENT_SOURCE_DIR = sys.argv[2]

src/gen-ragel-artifacts.py

@@ -6,10 +6,10 @@ import os, os.path, sys, subprocess, shutil, tempfile
 
 ragel = shutil.which ('ragel')
 if not ragel:
-	exit ('You have to install ragel if you are going to develop HarfBuzz itself')
+	sys.exit ('You have to install ragel if you are going to develop HarfBuzz itself')
 
 if len (sys.argv) < 4:
-	exit (__doc__)
+	sys.exit (__doc__)
 
 OUTPUT = sys.argv[1]
 CURRENT_SOURCE_DIR = sys.argv[2]