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/Makefile

@@ -10,6 +10,7 @@ all:
 		    -e	"s|@@XBPS_INSTALL_ETCDIR@@|$(ETCDIR)|g"		\
 		    -e  "s|@@XBPS_INSTALL_SHAREDIR@@|$(SHAREDIR)|g"	\
 		    -e  "s|@@XBPS_INSTALL_SBINDIR@@|$(SBINDIR)|g"	\
+		    -e	"s|@@XBPS_INSTALL_LIBEXECDIR@@|$(LIBEXECDIR)|g"	\
 			$$bin.sh.in > $$bin;				\
 	done
 	for dir in $(SUBDIRS); do			\