xbps-src: build binpkgs compressed with xz by default.

- Added two new options for xbps-src.conf:
    XBPS_COMPRESS_CMD by default set to xz.
    XBPS_COMPRESS_LEVEL by default not set.

Change these options to override the behaviour.

--HG--
extra : convert_revision : cbf096e3ff8c290ec0dfd96e5e7cf81f82cbf26a

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

@@ -8,14 +8,13 @@
 XBPS_INSTALLDIR=@@XBPS_INSTALL_PREFIX@@
 
 #
-# Global directory where the xbps distribution files are stored.
-# Templates, patches and helper files should all be in that directory.
+# Directory where you downloaded the GIT xbps-src/templates repository.
 #
 XBPS_DISTRIBUTIONDIR=$HOME/xbps
 
 #
-# Master directory: this is where all symlinks will be
-# created pointing at packages installed in XBPS_DESTDIR.
+# Master directory: this is where all packages files are copied from
+# XBPS_DESTDIR, to resolve dependencies.
 #
 XBPS_MASTERDIR=$XBPS_DISTRIBUTIONDIR/masterdir
 
@@ -57,6 +56,19 @@ XBPS_CXXFLAGS="$XBPS_CFLAGS"
 #
 XBPS_FETCH_CMD=wget
 
+#
+# Compression program used to build the binary packages.
+# Possible values: gzip, bzip2 or xz. Default xz.
+#
+XBPS_COMPRESS_CMD=xz
+
+#
+# Compression level used in XBPS_COMPRESS_CMD to build the
+# binary packages. Possible values: 1-9. If unset, default value
+# by the command will be used.
+#
+#XBPS_COMPRESS_LEVEL=9
+
 #
 # Cross compilation stuff.
 #