BUILD/MINOR: systemd: fix compiler warning about unused result

There is a compiler warning after commit 1b6e75fa84 ("MEDIUM: haproxy-
systemd-wrapper: Use haproxy in same directory"):

src/haproxy-systemd-wrapper.c: In function ‘locate_haproxy’:
src/haproxy-systemd-wrapper.c:28:10: warning: ignoring return value of ‘readlink’, declared with attribute warn_unused_result [-Wunused-result]

Fix the compiler warning by checking the return value of readlink().
BUILD: simplify the date and version retrieval in the makefile

The makefile currently uses some complex and non-always portable
methods to retrieve the date and version (eg: linux's date command).

For the date, we can use git log -1 --pretty=format:%ci instead of
date+sed. For the version, it's easier and safer to count single log
lines.

Note that the VERSION variable was wrong since it could contain the
version+subversion instead of just the version. This is now fixed by
adding --abbrev=0 in describe.
BUILD: prepare the makefile to skip format lines in SUBVERS and VERDATE

We're going to put format lines in these files for use by git archive,
so let's ensure that the current default format still works. For this
we'll use two lines and only take the first one without a format tag.
BUILD: use format tags in VERDATE and SUBVERS files

The first line now contains a git format tag asking git-archive to
place the last commit's commit date and the last commit's abbreviated
ID respectively. The makefile will use these information in preference
when they're available and git is not available.

Now it's only necessary to add the two following lines in
.git/info/attributes to have the files automatically filled by git-archive :

SUBVERS export-subst
VERDATE export-subst
BUG/MEDIUM: channel:  bo_getline() must wait for \n until buffer is full

We must not report incomplete data if the buffer is not full, otherwise
we can abort some processing on the stats socket when dealing with massive
amounts of commands.
CLEANUP: check: server port is unsigned

Baptiste Assmann reported some confusing printf() output of the server
port since it's declared signed. Better turn it to unsigned.

There's no need to backport this, it's only used in 16-bit places.
DOC: compression: chunk are not compressed anymore

Add the chunk issue to the list of non-working cases.
CLEANUP: code style: use tabs to indent codes

The original codes are indented by spaces and not aligned with the former line.
It should be a convention to indent by tabs in HAProxy.

Signed-off-by: Godbach <nylzhaowei@gmail.com>
DOC: checkcache: block responses with cacheable cookies

"requests" -> "responses"

Signed-off-by: Godbach <nylzhaowei@gmail.com>
BUG/MINOR: check_config_validity: check the returned value of stktable_init()

The function stktable_init() will return 0 if create_pool() returns NULL. Since
the returned value of this function is ignored, HAProxy will crash if the pool
of stick table is NULL and stksess_new() is called to allocate a new stick
session. It is a better choice to check the returned value and make HAProxy exit
with alert message if any error is caught.

Signed-off-by: Godbach <nylzhaowei@gmail.com>
Merge branch 'master' of http://git.1wt.eu/git/haproxy