MINOR: samples: Handle the type SMP_T_METH when we duplicate a sample in smp_dup

MINOR: samples: Handle the type SMP_T_METH when we duplicate a sample in smp_dup

First, the type SMP_T_METH was not handled by smp_dup function. It was never
called with this kind of samples, so it's not really a problem. But, this could
be useful in future.

For all known HTTP methods (GET, POST...), there is no extra space allocated for
a sample of type SMP_T_METH. But for unkown methods, it uses a chunk. So, like
for strings, we duplicate data, using a trash chunk.