Change pagedim from object to array

The usage of pagedim does not appear to make any use of its being an
object, such as setting non-numeric properties. If we can change it to
an array, it greatly simplifies _deletePage(), and doesn't break current
usage.

Author: Kenneth Glassey

jspdf.js

@@ -181,7 +181,7 @@ var jsPDF = (function(global) {
 			page = 0,
 			currentPage,
 			pages = [],
-			pagedim = {},
+			pagedim = [],
 			content = [],
 			lineCapID = 0,
 			lineJoinID = 0,