xbps-src: added suport for XBPS_CACHEDIR in configuration file.

XBPS_CACHEDIR will be bind mounted as read/write in target masterdir
into /cachedir. This directory must have read/write perms for the user
running xbps-src.

xbps-src/shutils/chroot.sh.in

@@ -31,14 +31,16 @@ trap "_umount && return $?" 0 INT QUIT TERM
 
 _mount()
 {
-	MASTERDIR="${XBPS_MASTERDIR}" ${sudo_cmd} \
+	MASTERDIR="${XBPS_MASTERDIR}" CACHEDIR="${XBPS_CACHEDIR}" \
+		${sudo_cmd} \
 		@@XBPS_INSTALL_LIBEXECDIR@@/xbps-src-chroot-helper mount
 	return $?
 }
 
 _umount()
 {
-	MASTERDIR="${XBPS_MASTERDIR}" ${sudo_cmd} \
+	MASTERDIR="${XBPS_MASTERDIR}" CACHEDIR="${XBPS_CACHEDIR}" \
+		${sudo_cmd} \
 		@@XBPS_INSTALL_LIBEXECDIR@@/xbps-src-chroot-helper umount
 	return $?
 }