xbps-src: repair and improve the bootstrap target (from scratch).

- There's no need to install rdeps into the masterdir, just base-files.
- There's no need to exit if XBPS_TARGET_PKG == sourcepkg, just return.
- After building base-chroot, install bootstrap binary packages.

xbps-src

@@ -248,6 +248,7 @@ install_bbotstrap() {
         fi
     fi
     mkdir -p $XBPS_MASTERDIR/var/db/xbps/keys
+    cd $XBPS_MASTERDIR
     cp -f $XBPS_COMMONDIR/repo-keys/*.plist $XBPS_MASTERDIR/var/db/xbps/keys
     ${_bootstrap_arch} xbps-install -S --repository=${XBPS_REPOSITORY} \
         ${XBPS_INSTALL_ARGS} -c ${XBPS_HOSTDIR}/repocache \
@@ -558,7 +559,9 @@ case "$XBPS_TARGET" in
         fi
         setup_pkg $XBPS_TARGET_PKG
         install_pkg $XBPS_TARGET
-        rm -f ${bootstrap_vpkg}
+        [ -d $XBPS_MASTERDIR ] && rm -rf $XBPS_MASTERDIR
+        unset XBPS_TARGET_PKG
+        install_bbotstrap
         ;;
     bootstrap-update)
         if [ -n "$CHROOT_READY" -a -z "$IN_CHROOT" ]; then