BUG/MEDIUM: samples: Fix handling of SMP_T_METH samples

BUG/MEDIUM: samples: Fix handling of SMP_T_METH samples

Samples of type SMP_T_METH were not properly handled in smp_dup(),
smp_is_safe() and smp_is_rw(). For "other" methods, for instance PATCH, a
fallback was performed on the SMP_T_STR type. Only the buffer considered
changed. "smp->data.u.meth.str" should be used for the SMP_T_METH samples
while smp->data.u.str should be used for SMP_T_STR samples. However, in
smp_dup(), the result was stored in wrong buffer, the string one instead of
the method one. In smp_is_safe() and smp_is_rw(), the method buffer was not
used at all.

We now take care to use the right buffer.

This patch must be backported to all stable versions.