usbhid-ups (CPS): determine battery.voltage scale factor at runtime

If the battery.voltage reading is greater than 1.4x battery.voltage.nominal,
apply a scale factor of 2/3 to bring the voltage back in line.

Closes networkupstools/nut#142
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