Fixed clang-3.4 unused function warnings in optimized builds like the following:
"""
../examples/energy/energy-model-example.cc:39:1: error: unused function
'PrintReceivedPacket' [-Werror,-Wunused-function]
PrintReceivedPacket (Address& from)
^
1 error generated.
"""
Implemented "if (false)" trick inside NS_LOG* macros for optimized builds.
"sizeof()" trick might be a little better but it produces the following
warning with clang-3.4:
"""
../examples/energy/energy-model-example.cc:39:1: error: function
'PrintReceivedPacket' is not needed and will not be emitted
[-Werror,-Wunneeded-internal-declaration]
PrintReceivedPacket (Address& from)
^
1 error generated.
"""
Macros from log.h, that depend on NS3_LOG_ENABLE, were moved to log-macros-enabled.h and log-macros-disabled.h to make log.h smaller.
