Changed to fixed-length frames (mostly untested).

api/net/sf/briar/api/crypto/AuthenticatedCipher.java

api/net/sf/briar/api/crypto/CryptoComponent.java

api/net/sf/briar/api/crypto/IvEncoder.java

api/net/sf/briar/api/plugins/InvitationConstants.java

api/net/sf/briar/api/transport/TransportConstants.java

components/net/sf/briar/crypto/AuthenticatedCipherImpl.java

components/net/sf/briar/crypto/CryptoComponentImpl.java

components/net/sf/briar/crypto/FrameIvEncoder.java

components/net/sf/briar/crypto/FramePeekingIvEncoder.java

...s/net/sf/briar/transport/ConnectionReaderFactoryImpl.java

components/net/sf/briar/transport/ConnectionReaderImpl.java

...s/net/sf/briar/transport/ConnectionWriterFactoryImpl.java

components/net/sf/briar/transport/ConnectionWriterImpl.java

components/net/sf/briar/transport/FrameEncoder.java

components/net/sf/briar/transport/FrameReader.java

components/net/sf/briar/transport/FrameWriter.java

...nents/net/sf/briar/transport/IncomingEncryptionLayer.java

...nents/net/sf/briar/transport/OutgoingEncryptionLayer.java

components/net/sf/briar/transport/TagEncoder.java

test/build.xml