[RELEASE] released 1.3.1 after resyncing with 1.2.15

[RELEASE] released 1.3.1 after resyncing with 1.2.15

Released 1.3.1 with the following changes from 1.2.15 :
   - now, haproxy warns about missing timeout during startup to try to
     eliminate all those buggy configurations.
   - added "Content-Type: text/html" in responses wherever appropriate, as
     suggested by Cameron Simpson.
   - implemented "option ssl-hello-chk" to use SSLv3 CLIENT HELLO messages to
     test server's health
   - implemented "monitor-uri" so that haproxy can reply to a specific URI with
     an "HTTP/1.0 200 OK" response. This is useful to validate multiple proxies
     at once.