BUG/MAJOR: http-ana: Get a fresh trash buffer for each header value replacement

BUG/MAJOR: http-ana: Get a fresh trash buffer for each header value replacement

When a "replace-header" action is used, we loop on all headers in the
message to change value of all headers matching a name. The new value is
placed in a trash. However, there is a race here because if the message must
be defragmented, another trash is used. If several defragmentation are
performed because several headers must be updated at same time, the first
trash, used to store the new value, may be crushed. Indeed, there are only 2
pre-allocated trash used in rotation. and the trash to store the new value
is never renewed. As consequece, random data may be inserted into the header
value.

Here, to fix the issue, we must take care to refresh the trash buffer when
we evaluated a new header. This way, a trash used for the new value, and
eventually another way for the htx defragmentation. But that's all.

Thanks to Christian Ruppert for his detailed report.

This patch must be to all stable versions. On the 2.0, the patch must be
applied on src/proto_htx.c and the function is named
htx_transform_header_str().