Feature request: relative paths

An svn feature that I used a lot is `svn cat some-file' -- and with git I can get close to that with `git show :some-file', except that unlike other paths, it must be an absolute path from the repository root. I could obviously make up a script that will do it, but that's just buying myself some time until I find some other command where I'll want to use it.

It looks like it would be relatively easy to do this, since when I do specify the relative path I get an error message suggesting the full one (provided that the relative path is simple -- no ".." etc). So, now that I can actually UTSL, I went there, and tried some half-assed hacking -- I made it so "::path" uses the prefix and normalizes the result, so, for example

  cd git/Documentation
  git show ::../Documentation/./user-manual.conf

works as expected. Using "::" looks bad IMO, and the hack I did is likely suffering from some problems, but overall it doesn't look too hard.