Added native utilities to mount/umount/chroot via capabilities(7).

Three new helpers will now be installed into ${libexecdir}:
 - xbps-src-capchroot needs to have set CAP_SYS_CHROOT ep.
 - xbps-src-chroot-cap{,u}mount: needs to have set CAP_SYS_ADMIN ep.

That means that libcap and setcap(8) are now required to install
xbps-src and use it as normal user.

--HG--
extra : convert_revision : 586d6526079e085f86bf3e393459d429f6f0ef99

xbps-src/etc/xbps-src.conf.in

@@ -44,19 +44,10 @@ XBPS_COMPRESS_CMD=xz
 #XBPS_PREFER_BINPKG_DEPS=yes
 
 #
-# Build packages with your unprivileged user in the chroot
-# via capchroot. The only required steps with privileges are
-# the bind mounts, a helper script (xbps-src-chroot-helper) needs
-# to be run with sudo for this task.
+# Build packages with your unprivileged user in the chroot thanks
+# to POSIX.1e Capabilities as explained in capabilities(7) on GNU/Linux.
 #
 # fakeroot is only used for the installation stage via the helper
 # script xbps-src-doinst-helper.
 #
-# capchroot allows ordinary users to use the chroot(2) syscall.
-# To make this work, uncomment this option and run the following
-# commands (as root):
-#
-# $ setcap cap_sys_chroot=ep /usr/bin/capchroot
-# $ echo "/path/to/masterdir $(whoami)" >> /etc/capchroot.allow
-#
 #XBPS_USE_CAPCHROOT=yes