Files with the same prefix in different dirs

The bug:

    ~% ls -1 test-dotfiles/**/*(.)
    test-dotfiles/tag-openbsdbox/zshrc_alias
    test-dotfiles/tag-openbsdbox/zshrc_bsd
    test-dotfiles/tag-zsh/zshrc
    ~% lsrc -t openbsdbox -t zsh -d test-dotfiles
    /home/mike/.zshrc_alias:/home/mike/test-dotfiles/tag-openbsdbox/zshrc_alias
    /home/mike/.zshrc_bsd:/home/mike/test-dotfiles/tag-openbsdbox/zshrc_bsd
    ~%

We expect to also see:

    /home/mike/.zshrc:/home/mike/test-dotfiles/tag-zsh/zshrc

This arises because we were checking for files the start with another
name, rather than a full equality.
Begin a basic test suite via cram
Ensure executables are so
Integrate the test suite with Make

- Tests can now be run with `make check`
Add testing information to CONTRIBUTING.md