libnih: enable threading; unbreak cross compilation.
Merge pull request #699 from onekk/master

New package: opencv 2.4.10 and accompaining packages
add CONTRIBUTING.md file.
CONTRIBUTING.md: fix typo
New package: cgmanager-0.33.
CONTRIBUTING.md: improve formating
opencv: unbreak x86; remove unnecessary rdeps; simplify.
stunnel: update to 5.08.
New package: sex-1.0
xbps-src: clean <pkgname> also removes pkg files in destdir.
xbps-src: improve clean description.
iputils: make ping{,6} setuid rather than using CAP_NET_RAW.

The reason is that we can't preserve capabilities when making
the rootfs tarballs.
New Package: libpgf-6.14.12