[RELEASE] Released version 1.3.15.8

[RELEASE] Released version 1.3.15.8

Released version 1.3.15.8 with the following main changes :
    - [BUG] Fix listen & more of 2 couples <ip>:<port>
    - [DOC] remove buggy comment for use_backend
    - [CRITICAL] fix server state tracking: it was O(n!) instead of O(n)
    - [BUG] "option transparent" is for backend, not frontend !
    - [BUG] we must not exit if protocol binding only returns a warning
    - [BUG] inform the user when root is expected but not set
    - [DOC] large doc update backported from mainline
    - [BUG] the "source" keyword must first clear optional settings
    - [BUG] global.tune.maxaccept must be limited even in mono-process mode
    - [BUG] typo in timeout error reporting : report *res and not *err