BUG/MEDIUM: prevent buffers being overwritten during build_logline() execution

BUG/MEDIUM: prevent buffers being overwritten during build_logline() execution

Calls to build_logline() are audited in order to use dynamic trash buffers
allocated by alloc_trash_chunk() instead of global trash buffers.

This is similar to commits 07a0fec ("BUG/MEDIUM: http: Prevent
replace-header from overwriting a buffer") and 0d94576 ("BUG/MEDIUM: http:
prevent redirect from overwriting a buffer").

This patch should be backported in 1.7, 1.6 and 1.5. It relies on commit
b686afd ("MINOR: chunks: implement a simple dynamic allocator for trash
buffers") for the trash allocator, which has to be backported as well.