Fix a bug in compilation caused by jdk version.(It works in
jdk 6 , but fail in jdk 7)

Because we use Sun's private api: com.sun.image.codec.jpeg, which
is not recommended to use. Use ImageIo api instead.
(see:http://www.oracle.com/technetwork/java/faq-sun-packages-142232.html)

During compiling , jdk 1.7 does not link with rt.jar(which contains
com.sun.image.codec.jpeg), so it complains it does not found symbol, instead it
uses special symbol file lib/ct.sym with class stubs. So we coerce it to
use the rt.jar by add a compilation option -XDignore.symbol.file .

So just add "<compilerArgument>-XDignore.symbol.file</compilerArgument>" to
maven-compiler-plugin in pom.xml to work around this.