BUG/MEDIUM: unique_id: junk in log on empty unique_id

When a request fail, the unique_id was allocated but not generated.
The string was not initialized and junk was printed in the log with %ID.

This patch changes the behavior of the unique_id. The unique_id is now
generated when a request failed.

This bug was reported by Patrick Hemmer.
BUG/MINOR: log: junk at the end of syslog packet

With a facily of 2 or 1 digit, the send size was wrong and bytes with
unknown value were sent.
The size was calculated using the start of the buffer and not the start
of the data which varies with the number of digits of the facility.

This bug was reported by Samuel Stoller and reported by Lukas Tribus.
DOC: add a mention about the limited chunk size

We now indicate that PD flags can be returned for chunk sizes >= 2GB.
MINOR: ssl: Add statement 'verifyhost' to "server" statements

verifyhost allows you to specify a hostname that the remote server's
SSL certificate must match. Connections that don't match will be
closed with an SSL error.