Merge xbps-src code to make it usable in a standalone mode.

The new xbps-src configuration file is `etc/conf` where you can
add your local overrides from defaults set via `etc/defaults.conf`.

To use this xbps-src, run these steps:

	$ make
	$ sudo make setup (to make chroot helper setgid)
	$ ./xbps-src ...

common/xbps-src/libexec/xbps-src-dopkg.sh

@@ -0,0 +1,62 @@
+#!//bin/bash
+#
+# Passed arguments:
+#	$1 - pkgname [REQUIRED]
+#	$2 - cross target [OPTIONAL]
+
+if [ $# -lt 1 -o $# -gt 2 ]; then
+	echo "$(basename $0): invalid number of arguments: pkgname [cross-target]"
+	exit 1
+fi
+
+PKGNAME="$1"
+XBPS_CROSS_BUILD="$2"
+
+. $XBPS_SHUTILSDIR/common.sh
+
+for f in $XBPS_COMMONDIR/helpers/*.sh; do
+	source_file "$f"
+done
+
+setup_pkg "$PKGNAME" $XBPS_CROSS_BUILD
+
+for f in $XBPS_COMMONDIR/environment/install/*.sh; do
+	source_file "$f"
+done
+
+XBPS_PKG_DONE="$wrksrc/.xbps_${PKGNAME}_${XBPS_CROSS_BUILD}_pkg_done"
+
+if [ -f $XBPS_PKG_DONE ]; then
+	exit 0
+fi
+
+#
+# Always remove metadata files generated in a previous installation.
+#
+for f in INSTALL REMOVE files.plist props.plist rdeps shlib-provides shlib-requires; do
+	[ -f ${PKGDESTDIR}/${f} ] && rm -f ${PKGDESTDIR}/${f}
+done
+
+# If it's a subpkg execute the pkg_install() function.
+if [ "$sourcepkg" != "$PKGNAME" ]; then
+	# Source all subpkg environment setup snippets.
+	for f in ${XBPS_COMMONDIR}/environment/setup-subpkg/*.sh; do
+		source_file "$f"
+	done
+	${PKGNAME}_package
+	pkgname=$PKGNAME
+
+	install -d $PKGDESTDIR
+	if declare -f pkg_install >/dev/null; then
+		export XBPS_PKGDESTDIR=1
+		run_func pkg_install
+	fi
+fi
+
+setup_pkg_depends $pkgname
+
+run_pkg_hooks post-install
+
+touch -f $XBPS_PKG_DONE
+
+exit 0