Fix error when raising without an Exception.

Raising without a valid exception is invalid:

>>> raise
Traceback (most recent call last):
  File "<stdin>", line 1, in <module>
TypeError: exceptions must be old-style classes or derived from BaseException, not NoneType
>>> raise Exception
Traceback (most recent call last):
  File "<stdin>", line 1, in <module>
Exception

Changing this to "raise Exception" fixes this problem.
PyNUT: Create a custom exception class.

This maintains backwards compatibility, and allows calling programs to
use "except PyNUTError" instead of "except Exception" when using PyNUT
methods.

See https://wiki.python.org/moin/HandlingExceptions for more
information.
Change format of raise keyword.

Fixes PyNUT Python 3 compatibility.
Added author information, bumped version.

According to the semantic versioning scheme (http://semver.org/), adding
features that do not break backwards compatibility with previous
releases means that the minor version number should be incremented.
Fixed version description.
Test presence of xsltproc for manpages doc generation.
Test presence of xmllint for manpages doc generation.
Merge branch 'pull_146' (xsltproc/xmllint detection)
conf/: fix parallel install

Do not reference the upsmon.conf.sample twice, otherwise install, with
a high number of make jobs, may fail, like so:
    http://autobuild.buildroot.net/results/256/2567e13cd5bc702bc3a38a1d6fc8e34022cc7db5/build-end.log

Signed-off-by: "Yann E. MORIN" <yann.morin.1998@free.fr>

---
This is not a rare occurence, as my testing managed to trigger the
issue in about 1 test out of 10 on average, on a not-so-fast machine.
udev: ignore 62-nut-usbups.rules

Follow-up commit to networkupstools/nut#140
nut-usbinfo: change link from Alioth SVN to GitHub
95-upower-hid.rules: updated by nut-usbinfo.pl

URL updated in previous commit.
nut-usbinfo: fix FreeBSD devd.conf to use $cdev
docs: update links for two articles
HCL: Mecer ME-100-WTU with blazer_usb

USB VID:PID = 0665:5161

Tested by @silvec (Oliver Sauder) on NUT 2.6.3

Reference: https://github.com/networkupstools/nut/issues/148
HCL: Belkin Regulator PRO-USB 050d:0f51 (0.17)

https://github.com/networkupstools/nut/issues/149
Fix typo error in nut-scanner doc

The example network range scanned when using 192.168.0.0/25 is actually
192.168.0.0 to 192.168.0.12*7* not (i.e. not .128) as previously stated
(reported by Evgeny 'Jim' Klimov)

Closes networkupstools/nut#144
docs: recommend I2C bus name for asem driver
nutdrv_qx: prevent a vicious loop when unexpected answers happen

If a 'QX_FLAG_QUICK_POLL' item gets an unexpected (non-empty) answer and, after returning from 'qx_ups_walk()', it is not followed by at least one item using a different 'command', the driver will loop endlessly using the same 'broken' answer instead of trying to get a new one from the UPS.
To solve this issue, make sure to have an empty 'previous_item' when starting 'qx_ups_walk()'.
Also, bail out of 'qx_ups_walk()' when a 'QX_FLAG_QUICK_POLL' item can't be preprocessed properly through 'ups_infoval_set()'.
docs: Add link to Roger Price's openSUSE writeup