Change Fopen() mode param to always include 'b'

'b' does nothing in UNIX, but does under Windows, where it specifies 'b'inary, and won't do any text line ending conversions. By always specifying 'b' we have one less behaviour difference between platforms.

Used the following regexes to make these changes:

vtksys::SystemTools::Fopen(.)"r" vtksys::SystemTools::Fopen(.)"w"