Issue with refs accros junctions

Summary

There seems to be a issue with junctions.

Steps to reproduce

I clone https://gitlab.com/willsalmon/buildstream-kicad

I run: bst track kicad.bst bst build kicad.bst

Interestingly if you track the junctions before running

bst build kicad.bst

Then you get different errors.

What is the current bug behavior?

Bst exits because that the ref's do not match.

What is the expected correct behavior?

It should down load all of the dependencies and try to build them

(I dont think the project will build atm but it should at least try. And it is not getting close.)

Relevant logs and/or screenshots

https://hastebin.com/odegehogaq.md

[00:00:24][784d4223][fetch:freedesktop-sdk.bst:base/gnutls.bst] WARNING Try #2 failed, retrying
[--:--:--][784d4223][fetch:freedesktop-sdk.bst:base/gnutls.bst] START   base-sdk/base-gnutls/784d4223-fetch.15971.log
[--:--:--][784d4223][fetch:freedesktop-sdk.bst:base/gnutls.bst] START   Fetching https://www.gnupg.org/ftp/gcrypt/gnutls/v3.6/gnutls-3.6.2.tar.xz
[00:00:26][593520fe][fetch:freedesktop-sdk.bst:base/gnupg.bst] FAILURE Fetching https://www.gnupg.org/ftp/gcrypt/gnupg/gnupg-2.2.8.tar.bz2
[00:00:26][593520fe][fetch:freedesktop-sdk.bst:base/gnupg.bst] FAILURE File downloaded from https://www.gnupg.org/ftp/gcrypt/gnupg/gnupg-2.2.8.tar.bz2 has sha256sum '777b4cb8ced21965a5053d4fa20fe11484f0a478f3d011cef508a1a49db50dcd', not '747e1632271bd6aa852b9c40be15a12614adad257e4a765261355812d110558e'!

    Printing the last 20 lines from log file:
    /home/will/.cache/buildstream/logs/base-sdk/base-gnupg/593520fe-fetch.15969.log
    ======================================================================

        CFLAGS: -O2 -g -fstack-protector-strong
        CPPFLAGS: -O2 -D_FORTIFY_SOURCE=2
        CXXFLAGS: -O2 -g -fstack-protector-strong
        HOME: /tmp
        LC_ALL: en_US.UTF-8
        LDFLAGS: -fstack-protector-strong -Wl,-z,relro,-z,now
        LOGNAME: tomjon
        MAKEFLAGS: -j4
        PATH: /usr/bin:/bin:/usr/sbin:/sbin
        SHELL: /bin/sh
        SOURCE_DATE_EPOCH: '1320937200'
        TERM: dumb
        TZ: UTC
        USER: tomjon
        USERNAME: tomjon
        V: '1'
    [--:--:--] START   base/gnupg.bst-0: Fetching https://www.gnupg.org/ftp/gcrypt/gnupg/gnupg-2.2.8.tar.bz2
    [00:00:26] FAILURE base/gnupg.bst-0: Fetching https://www.gnupg.org/ftp/gcrypt/gnupg/gnupg-2.2.8.tar.bz2
    [00:00:26] FAILURE base/gnupg.bst: File downloaded from https://www.gnupg.org/ftp/gcrypt/gnupg/gnupg-2.2.8.tar.bz2 has sha256sum '777b4cb8ced21965a5053d4fa20fe11484f0a478f3d011cef508a1a49db50dcd', not '747e1632271bd6aa852b9c40be15a12614adad257e4a765261355812d110558e'!
    ======================================================================

Other relevant information

• BuildStream version affected: current master ie. f62b6cb7

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