MEDIUM: ssl: add mapping from SNI to cert file using "crt-list"

It designates a list of PEM file with an optional list of SNI filter
per certificate, with the following format for each line :

    <crtfile>[ <snifilter>]*

Wildcards are supported in the SNI filter. The certificates will be
presented to clients who provide a valid TLS Server Name Indication
field matching one of SNI filter. If no SNI filter is specified the
CN and alt subjects are used.
BUG/MEDIUM: ssl: improve error processing and reporting in ssl_sock_load_cert_list_file()

fe61656b added the ability to load a list of certificates from a file,
but error control was incomplete and misleading, as some errors such
as missing files were not reported, and errors reported with Alert()
instead of memprintf() were inappropriate and mixed with upper errors.
Also, the code really supports a single SNI filter right now, so let's
correct it and the doc for that, leaving room for later change if needed.
BUILD: add explicit support for TFO with USE_TFO

TCP Fast Open is supported in server mode since Linux 3.7, but current
libc's don't define TCP_FASTOPEN=23. Introduce the new USE flag USE_TFO
to define it manually in compat.h. Also note this in the TFO related
documentation.