Always block SIGPIPE globally

OpenSSL and GnuTLS are still causing this problem (although FFmpeg could
be blamed as well - but not really). In particular, it was happening to
libmpv users and in cases the pseudo-gui profile is used. This was
because all signal handling is in the terminal code, so if terminal is
disabled, it won't be set. This was obviously a questionable shortcut.

Avoid further problems by always blocking the signal. This is done even
for libmpv, despite our policy of not messing with global state.

Explicitly document this in the libmpv docs. It turns out that a version
bump to 1.17 was forgotten for the addition of MPV_FORMAT_BYTE_ARRAY, so
document that change as part of 1.16.

DOCS/client-api-changes.rst

@@ -25,10 +25,11 @@ API changes
 
 ::
 
+ 1.17   - mpv_initialize() now blocks SIGPIPE (details see client.h)
  --- mpv 0.9.0 is released ---
- 1.17   - add MPV_FORMAT_BYTE_ARRAY
  1.16   - add mpv_opengl_cb_report_flip()
         - introduce mpv_opengl_cb_draw() and deprecate mpv_opengl_cb_render()
+        - add MPV_FORMAT_BYTE_ARRAY
  1.15   - mpv_initialize() will now load config files. This requires setting
           the "config" and "config-dir" options. In particular, it will load
           mpv.conf.