Fixed jsamp sign algorithm for Java 1.7

When running on Java 1.7, the SPLAT fails to start because of signature
of jsamp library:

java.lang.SecurityException: invalid SHA1 signature file digest
Fixed invalid encoding in TAMFITS

The build was failing because of invalid encoding of the TAMFITS's
source code.
Fixed build error in TOPCAT

The build was failing because of wrong return data type of
uk.ac.starlink.topcat.SyntheticColumnQueryWindow.getType().

FIX: the method is public, so it could fail during runtime
Refactoring: Frog's JPEGUtility

The build was failing because of Sun's proprietary package
(com.sun.image.codec.jpeg) dependency. This package was removed from JDK
1.7.

Fixed by rewriting the code to use the standard JDK tools.