BUG/MEDIUM: lua: sample fetches based on response doesn't work

BUG/MEDIUM: lua: sample fetches based on response doesn't work

The direction (request or response) is not propagated in the
sample fecthes called throught Lua. This patch adds the direction
status in some structs (hlua_txn and hlua_smp) to make sure that
the sample fetches will be called with all the information.

The converters can not access to a TXN object, so there are not
impacted the direction. However, the samples used as input of the
Lua converter wrapper are initiliazed with the direction. Thereby,
the struct smp stay consistent.
[wt: needs to be backported to 1.6]