Add experimental warnings to the XMEGA and UC3 architectures when used in Atmel Studio 6.1.

git-svn-id: http://lufa-lib.googlecode.com/svn@2676 d5102386-fcda-11dd-9fdb-3debd5008f28
LUFA-IAR-Port: Merge in latest trunk.

git-svn-id: http://lufa-lib.googlecode.com/svn@2677 d5102386-fcda-11dd-9fdb-3debd5008f28
XMEGA-Demo-Ports: Merge in latest trunk.

git-svn-id: http://lufa-lib.googlecode.com/svn@2678 d5102386-fcda-11dd-9fdb-3debd5008f28