[PATCH consfigurator v3] DATA.ASDF:SYSTEM-VERSION-FILES support systems with version files

[Russell Sim]

Hey,

Seems this problem is more pervasive than I previously thought, while
trying to use the ten library[1] to do templating for configuration
files. I found they are using reader macros to load the readme as a long
description.

Example:

  :long-description
  #.(uiop:read-file-string
     (uiop:subpathname *load-pathname* "README.md"))

So even thought this patch fixes projects whose version is stored in
files, it seems that potentially anything could be in any arbitrary
file.

What do you think the best way to deal with this issue is?  I was
thinking it might make more sense to instead just tar the entire system
directory rather than being picky about which files are taken?

1. https://github.com/mmontone/ten/blob/master/ten.asd#L17-L18

Cheers,
Russell