[RELEASE] Released version 1.8-rc2

[RELEASE] Released version 1.8-rc2

Released version 1.8-rc2 with the following main changes :
    - BUG/MINOR: send-proxy-v2: fix dest_len in make_tlv call
    - BUG/MINOR: send-proxy-v2: string size must include ('\0')
    - MINOR: mux: Only define pipe functions on linux.
    - MINOR: cache: Remove useless test for nonzero.
    - MINOR: cache: Don't confuse act_return and act_parse_ret.
    - BUG/MEDIUM: h2: don't try to parse incomplete H1 responses
    - BUG/MEDIUM: checks/mux: always enable send-polling after connecting
    - BUG/MAJOR: fix deadlock on healthchecks.
    - BUG/MINOR: thread: fix a typo in the debug code
    - BUILD: shctx: allow to be built without openssl
    - BUG/MEDIUM: cache: don't try to resolve wrong filters
    - BUG/MAJOR: buffers: fix get_buffer_nc() for data at end of buffer
    - BUG/MINOR: freq: fix infinite loop on freq_ctr_period.
    - BUG/MINOR: stdarg.h inclusion
    - BUG/MINOR: dns: fix missing lock protection on server.
    - BUG/MINOR: lua: fix missing lock protection on server.
    - BUILD: enable USE_THREAD for OpenBSD build.
    - BUG/MAJOR: mux_pt: don't dereference a connstream after ->wake()
    - MINOR: thread: report multi-thread support in haproxy -vv