Don't create a new ClassWriter instance in toByteArray, in order for this code to work with subclasses.

Fixed bug in MethodNode (infinite loops when trying to copy a MethodNode into another several times).
Added unit test for this case (failing without the bug fix).
 

Added checks for abstract methods.

- split the ClassReader accept() method into several methods (readField, readMethod, readCode, readFrame, etc), each using local variables with the smallest possible scope. Required the addition of a Context helper class. Makes the code more readable, a little bit bigger (+4%), but also faster (1.12 speedup for the deserialize performance test).
- switched to the Java code style conventions, applied Eclipse auto format on all files.

- cleaned-up the tests relying on the JVM verifier (with JDK7 fallback to old verifier is no longer done for classes whose version is 1.7)
- added test to check that there is indeed no fallback to the old verifier (using a class without frames whose version is 1.7)

Moved checkClassSignature, checkMethodSignature and checkFieldSignature to CheckClassAdapter and made them public.

Workaround to make JarJar work, despite its incorrect use of the ASM API. A proper solution would be fix JarJar itself.