DOC: mention that Squid correctly responds 400 to PPv2 header

Amos reported that Squid builds 3.5.0.0_20140624 and 3.5.0.0_20140630
were confirmed to respond correctly here and that any version will do
the same.
(cherry picked from commit 9e1382002aa1ba12dcc637870befd077ff887aad)
DOC: fix typo in Unix Socket commands

Konstantin Romanenko reported a typo in the HTML documentation. The typo is
already present in the raw text version : the "shutdown sessions" command
should be "shutdown sessions server".
(cherry picked from commit e63a1eb290a1c407453dbcaa16535c85a1904f9e)
BUG/MEDIUM: ssl: Fix a memory leak in DHE key exchange

OpenSSL does not free the DH * value returned by the callback specified with SSL_CTX_set_tmp_dh_callback(),
leading to a memory leak for SSL/TLS connections using Diffie Hellman Ephemeral key exchange.
This patch fixes the leak by allocating the DH * structs holding the DH parameters once, at configuration time.

Note: this fix must be backported to 1.5.
(cherry picked from commit 8de5415b85512da871d58d1e9a0a33bd67f3b570)
BUG/MINOR: http: base32+src should use the big endian version of base32

We're using the internal memory representation of base32 here, which is
wrong since these data might be exported to headers for logs or be used
to stick to a server and replicated to other peers. Let's convert base32
to big endian (network representation) when building the binary block.

This mistake is also present in 1.5, it would be better to backport it.
(cherry picked from commit 5ad6e1dc09f0a85aabf86f154b1817b9ebffb568)
BUG/MEDIUM: connection: fix memory corruption when building a proxy v2 header

Use temporary trash chunk, instead of global trash chunk in
make_proxy_line_v2() to avoid memory overwrite.

This fix must also be backported to 1.5.
(cherry picked from commit 77d1f0143e210c13ee8ec6aaf6b3150fa4ce6c5b)
BUG/MEDIUM: connection: fix proxy v2 header again!

Last commit 77d1f01 ("BUG/MEDIUM: connection: fix memory corruption
when building a proxy v2 header") was wrong, using &cn_trash instead
of cn_trash resulting in a warning and the client's SSL cert CN not
being stored at the proper location.

Thanks to Lukas Tribus for spotting this quickly.

This should be backported to 1.5 after the patch above is backported.
(cherry picked from commit 3b9a0c9d4d083d749846d66f9bd4caabafe4ee78)
[RELEASE] Released version 1.5.3

Released version 1.5.3 with the following main changes :
    - DOC: fix typo in Unix Socket commands
    - BUG/MEDIUM: connection: fix memory corruption when building a proxy v2 header
    - BUG/MEDIUM: ssl: Fix a memory leak in DHE key exchange
    - DOC: mention that Squid correctly responds 400 to PPv2 header
    - BUG/MINOR: http: base32+src should use the big endian version of base32
    - BUG/MEDIUM: connection: fix proxy v2 header again!
Merge tag 'v1.5.3'
Merge branch 'master' into ddos