BUG/MEDIUM: http: fix improper parsing of HTTP methods for use with ACLs

pat_parse_meth() had some remains of an early implementation attempt for
the patterns, it initialises a trash and never sets the pattern value there.
The result is that a non-standard method cannot be matched anymore. The bug
appeared during the pattern rework in 1.5, so this fix must be backported
there. Thanks to Joe Williams of GitHub for reporting the bug.
BUG/MINOR: pattern: remove useless allocation of unused trash in pat_parse_reg()

Just like previous patch, this is a remains of an early implementation. Also
fix the outdated comments above. The fix may be backported to 1.5 though the
bug cannot be triggerred, thus it's just a matter of keeping the code clean.
BUG/MEDIUM: acl: correctly compute the output type when a converter is used

Sample expressions involving converters in expression simply do not work
if the converter changes the sample type from the original keyword. Either
the keyword is a sample fetch keyword and its own type is used, or it's an
ACL keyword, and the keyword's parse/index/match functions are used despite
the converters. Thus it causes such a stupid error :

     redirect location / if { date,ltime(%a) -i Fri }

[ALERT] 240/171746 (29127) : parsing [bug-conv.cfg:35] : error detected in proxy 'svc' while parsing redirect rule : error in condition: 'Fri' is not a number.

In fact now in ACLs, the case where the ACL keyword is alone is an exception
(eventhough the most common one). It's an exception to the sample expression
parsing rules since ACLs allow to redefine alternate parsing functions.

This fix does two things :
  - it voids any references to the ACL keyword when a converter is involved
    since we certainly not want to enforce a parser for a wrong data type ;
  - it ensures that for all other cases (sample expressions), the type of
    the expression is used instead of the type of the fetch keyword.

A significant cleanup of the code should be done, but this patch only aims
fixing the bug.

The fix should be backported into 1.5 since this appeared along the redesign
of the acl/pattern processing.
CLEANUP: acl: cleanup some of the redundancy and spaghetti after last fix

This code aims at clearing up the ACL parsing code a bit to make it
more obvious what happens in the case of an ACL keyword and what happens
in the case of a sample expression. Variables prev_type and cur_type were
merged, and ACL keyword processing functions are checked only once.

This patch could be backported into 1.5 after the previous patch, in order
to keep the code more maintainable.
BUG/MEDIUM: auth: fix segfault with http-auth and a configuration with an unknown encryption algorithm

Grégoire Morpain reported a segfault when a secured password is used for http
authentication. It was caused by the use of an unsupported encryption algorithm
with libcrypto. In this case, crypt() returns a NULL pointer.

The fix should be backported to 1.4 and 1.5.
BUG/MEDIUM: config: userlists should ensure that encrypted passwords are supported

When an unknown encryption algorithm is used in userlists or the password is
not pasted correctly in the configuration, http authentication silently fails.

An initial check is now performed during the configuration parsing, in order to
verify that the encrypted password is supported. An unsupported password will
fail with a fatal error.

This patch should be backported to 1.4 and 1.5.
BUG/CRITICAL: http: don't update msg->sov once data start to leave the buffer

Commit bb2e669 ("BUG/MAJOR: http: correctly rewind the request body
after start of forwarding") was incorrect/incomplete. It used to rely on
CF_READ_ATTACHED to stop updating msg->sov once data start to leave the
buffer, but this is unreliable because since commit a6eebb3 ("[BUG]
session: clear BF_READ_ATTACHED before next I/O") merged in 1.5-dev1,
this flag is only ephemeral and is cleared once all analysers have
seen it. So we can start updating msg->sov again each time we pass
through this place with new data. With a sufficiently large amount of
data, it is possible to make msg->sov wrap and validate the if()
condition at the top, causing the buffer to advance by about 2GB and
crash the process.

Note that the offset cannot be controlled by the attacker because it is
a sum of millions of small random sizes depending on how many bytes were
read by the server and how many were left in the buffer, only because
of the speed difference between reading and writing. Also, nothing is
written, the invalid pointer resulting from this operation is only read.

Many thanks to James Dempsey for reporting this bug and to Chris Forbes for
narrowing down the faulty area enough to make its root cause analysable.

This fix must be backported to haproxy 1.5.
Merge branch 'master' of http://git.1wt.eu/git/haproxy