Ensure the "errstr" buffer is always 0-terminated

Coverity CID#1238651 (and many others)
Ensure pidftemplate is always 0-terminated

Coverity CID#1238650
Clear ai on return, also in case of error

Coverity CID#1238644
add missing include syslog.h
Fix obi-wan (whoops)
Pass whole struct sockaddr to function address_matches() and use it to
compare against the masks defined in auth file.
Update clientacl.c

Update test code with new prototype of address_matches()
Implement new config file option "cowdir"

Allows to specify a location where copy-on-write files should be
written.
Revert "Enable automatic coverity coverage"

This reverts commit eb6365af2c4c8eecf62317940c06f2bc58810a98.

The travis stuff isn't supposed to work that way; also, we're doing
weekly coverity builds with buildbot now, so it's less relevant.
Update nbd-server.c

Added a parameter to output a version string.
Replace return by break statement

Both are extraneous, really, but keep the break there for consistency (and to
avoid "eep, forgot... ah, no" kind of things)

Using return instead (without argument) makes clang choke, which is useless.
Fix various warnings that pop up by default with gcc 4.9
Document -V option
Make short version of -V actually work
Wire gznbd into general configure.ac/Makefile.am

Add --enable-gznbd configure option (disabled by default).
Avoid multiple recompilations of cliserv.c by factoring it into a static
library.

This fixes gznbd compilation broken after
43b96ec0d22c0a42c20104cb66aa2d2236da3e77:

gznbd.c:(.text.startup+0x420): undefined reference to `ntohll'
gznbd: use atoll() to convert size argument

gznbd works incorrectly with large size argument which overflows 32-bit integer.

For example:
gznbd /dev/nbd0 /root/test.gz 1000204886016
gznbd: 1000204886016 does not appear to be a valid size

The size is stored in u64, but is converted from a string using atol().
Simply replace atol() with atoll().
gznbd is compiled with -std=gnu99 (as the whole nbd), so atoll() is available.

Links to the original patch:
[1] https://sourceforge.net/p/nbd/mailman/nbd-general/thread/560411311771602%40web126.yandex.ru/#msg27860052
[2] http://marc.info/?l=nbd-general&m=131177162001072&w=2