xbps-src: add -m flag and make-repoidx target.

* -m flag to specify a custom XBPS_MASTERDIR, overwritting the value
  from xbps-src.conf.
* make-repoidx target to create a package index plist file for
  the local repository associated with a masterdir, or one specified
  by the -p flag.

--HG--
extra : convert_revision : dbd502b532fd49cd17a79a187488a1e92f361ee0

xbps-src/libexec/xbps-src-doinst-helper.sh.in

@@ -27,6 +27,11 @@
 PKG_TMPLNAME="$1"
 
 . @@XBPS_INSTALL_ETCDIR@@/xbps-src.conf
+
+if [ -n "${MASTERDIR}" ]; then
+	export XBPS_MASTERDIR="${MASTERDIR}"
+fi
+
 . @@XBPS_INSTALL_SHAREDIR@@/shutils/init_funcs.sh
 
 set_defvars