Replace URL for libxml2

[TheDearbear]

Hello! URL for libxml2 is no longer valid and returns error 404.

ps3libraries/scripts/012-libxml2-2.7.8.sh

Line 5 in 3047d86

wget --continue http://xmlsoft.org/download/libxml2-2.7.8.tar.gz

Working URL for the library is http://xmlsoft.org/sources/libxml2-2.7.8.tar.gz