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/chroot/repos-local.conf

@@ -0,0 +1,3 @@
+# Local repositories
+repository=/host/binpkgs
+repository=/host/binpkgs/nonfree

common/xbps-src/chroot/repos-remote.conf

@@ -0,0 +1,3 @@
+# Remote repositories
+repository=http://repo.voidlinux.eu/current
+repository=http://repo.voidlinux.eu/current/nonfree

common/xbps-src/chroot/xbps.conf

@@ -0,0 +1,68 @@
+# Configuration file for XBPS.
+#
+# - Lines starting with # are ignored.
+# - Values are set after the equal sign, and don't accept blanks nor newlines.
+
+# Set root directory, by default set to /. This expects an absolute path.
+#rootdir=/
+
+# Set cache directory, if starts with / it's an absolute path,
+# otherwise it's relative to rootdir.
+cachedir=/host/repocache
+
+# comment it out to disable syslog logging.
+#syslog=true
+
+## REPOSITORIES
+#
+# Local or remote repositories are accepted.
+#
+#  - Local repositories expect an absolute path to the directory that stores
+#    the <arch>-repodata file.
+#  - Accepted protocols for remote repositories: ftp, http or https.
+#  - Repositories are added in the order in which are specified (top->bottom).
+#
+#repository=http://repo.voidlinux.eu/current
+
+# Uncomment this one for "non-free" packages.
+#repository=http://repo.voidlinux.eu/current/nonfree
+
+# REPOSITORY MIRRORS
+#repository=http://repo2.voidlinux.eu/current
+#repository=http://repo2.voidlinux.eu/current/nonfree
+#
+#repository=http://xbps.nopcode.org/repos/current
+#repository=http://xbps.nopcode.org/repos/current/nonfree
+
+## VIRTUAL PACKAGES
+#
+# Virtual package overrides. You can set your own list of preferred virtual
+# packages in your system. This expects two arguments separated by a colon:
+#  <vpkgver>:<realpkgname>.
+#
+# - <vpkgver> means "virtual package name" and "version/revision"
+#   separated by a dash, i.e 'foo-1.0_1".
+# - <realpkgname> means a real package name (without any version).
+#
+# By default we prefer the `dcron` package as default cron daemon.
+#virtualpkg=cron-daemon-0_1:dcron
+
+# Sets the virtual package directory looking for .vpkg files with
+# virtual package settings (by using the `virtualpkg' keyword).
+#
+# If starts with / it's an absolute path, otherwise it's relative to rootdir.
+# By default it's set to <rootdir>/etc/xbps/virtualpkg.d.
+#virtualpkgdir=etc/xbps/virtualpkg.d
+
+# You can also include additional files by using the "include" keyword.
+# This expects an absolute path to a file.
+#include=/path/to/another/file.conf
+#
+# Alternative repos
+include=/etc/xbps/repos/alternative.conf
+
+# Local repos
+include=/etc/xbps/repos/local.conf
+
+# Remote repos
+include=/etc/xbps/repos/remote.conf