In Joey's master branch, `CHANGELOG` is a real file, whereas previously it was a symlink.  This breaks the `/usr/src/propellor` newer version check.

Steps to reproduce:

1. Install propellor 3.2.3 or older with apt on Debian or Ubuntu
2. `propellor --init` and select option `A`
3. Prepare a pseudorelease: merge Joey's master branch into [my Debian packaging branch](https://git.spwhitton.name/?p=propellor.git;a=shortlog;h=refs/heads/debian), `dch -v3.2.3+gitYYYYMMDD.fffffff`, `dpkg-buildpackage -uc -b`, `debi -u`
4. `propellor --spin`

I haven't yet tried reproducing this by building a `.deb` from Joey's master branch, rather than my packaging branch.  If the problem does not appear using a `.deb` from Joey's master branch, this is an internal Debian problem, rather than an upstream bug.  However, perhaps Joey can immediately see a solution.

Sample output:

    Auto-merging src/wrapper.hs
    Auto-merging src/Utility/UserInfo.hs
    Auto-merging src/Utility/SystemDirectory.hs
    Auto-merging src/Utility/Misc.hs
    Auto-merging src/Utility/FileSystemEncoding.hs
    Auto-merging src/Utility/Exception.hs
    Auto-merging src/Propellor/Types/CmdLine.hs
    Auto-merging src/Propellor/Shim.hs
    Auto-merging src/Propellor/Property/Gpg.hs
    Auto-merging src/Propellor/Property/Debootstrap.hs
    Auto-merging src/Propellor/Property.hs
    Auto-merging src/Propellor/PrivData.hs
    Auto-merging src/Propellor/Gpg.hs
    Auto-merging src/Propellor/CmdLine.hs
    Auto-merging debian/changelog
    Auto-merging CHANGELOG
    CONFLICT (add/add): Merge conflict in CHANGELOG
    Automatic merge failed; fix conflicts and then commit the result.
    propellor: Failed to run git ["merge","c590ddd8e2fa87baa409b6c29501d4473555ecfb","-s","recursive","-Xtheirs","--quiet","-m","merging upstream version","--allow-unrelated-histories"]
    CallStack (from HasCallStack):
      error, called at src/Propellor/DotDir.hs:425:17 in main:Propellor.DotDir

--spwhitton
