2fc46e18 broke running ./git-annex test
when git-annex-shell is not in PATH from another install, and also
caused the wrong git-annex-shell to be tested.

Using a symlink made programPath return the .cabal/ directory where the
git-annex binary is, but git-annex-shell is not in that directory.
Changing to a hard link avoids that problem.

Sponsored-by: Dartmouth College's Datalad project