Add -sigalg and -digestalg options for jarsigner to be able to sign an apk in jdk 7

The default digest algorithm of jarsigner for Java 1.7 is SHA256withRSA which isn't supported in Android, while for Java 1.6 it's MD5withRSA
So "-sigalg SHA1withRSA -digestalg SHA1" options are needed to sign correctly in jdk 7.

See this discussion for more details.

http://stackoverflow.com/questions/8739564/what-is-the-difference-between-the-java-1-6-and-1-7-jarsigner