Fix detection and drawing of whitespace-only changed blocks

Based on TortoiseSVN revision 24100

Signed-off-by: Sup Yut Sum <ch3cooli@gmail.com>
Fix diff-xls.js error reported from http://tortoisesvn.tigris.org/ds/viewMessage.do?dsForumId=4061&dsMessageId=3053016

Based on TortoiseSVN revision 24102

Signed-off-by: Sup Yut Sum <ch3cooli@gmail.com>