AMQP-CPP 2.6.1

• Correctly remove the dependency files on clean and fix frame errors on architectures where chars default to unsigned.
• Make it compile with cmake 2.8/gcc 4.7.3
• Don't ignore a given PREFIX in makefile.
• Fix undefined behaviour due to a reference to a destroyed temporary object.
• Correct the returning type of Connection::waiting()
• The returning type of Connection::waiting() should be bool, but currently it's size_t type.
• Made some destructors virtual and fixed a user-after-free bug.
• Correct the returning type of Connection::waiting()
• Add ln --relative to Makefile (install target)
• Make sure single gets are processed correctly.
• Changed writev to sendmsg to prevent SIGPIPE errors.