xbps-src: added new funcs to install files into DESTDIR.

vcopy <files> <targetdir>
	Executes cp -a <files> ${DESTDIR}/<targetdir>

vinstall <file> <mode> <targetdir> <targetfile>
	4th argument is optional.
	Executed install -Dm<mode> <file> ${DESTDIR}/<targetdir>/<file>

vmkdir <dir> <mode>
	Executed install -dm<mode> ${DESTDIR}/<dir>

xbps-src/shutils/tmpl_funcs.sh.in

@@ -284,6 +284,8 @@ set_tmpl_common_vars()
 {
 	[ -z "$pkgname" ] && return 1
 
+	. ${XBPS_SHUTILSDIR}/install_files.sh
+
 	FILESDIR=$XBPS_SRCPKGDIR/$pkgname/files
 	PATCHESDIR=$XBPS_SRCPKGDIR/$pkgname/patches
 	DESTDIR=${XBPS_DESTDIR}/${pkgname}-${version}