Fix issue when reading symlink during tar Archive

[technicianted]

This PR fixes an issue when create tar archives with symbolic links.

The code uses the Name() value to call os.Readlink(). This does not work since this value is only the name of the link. not the full path.

To resolve this, we need to pass down the original full FS path and use it during os.* calls.

Fixes #202

[mholt]

Thanks. Is there a test case that exhibits the bug? Or a related issue already reported?

[technicianted]

#202

[mholt]

Ah, thanks. I'm willing to merge this, but first, would it be an easy task to add a file to the test corpus which exhibits the behavior? If it is too complicated or something, let me know, but it'd be nice to be able to verify that the fix is working with a test.

[nishant-handa]

@mholt any updates on getting this in?
Will highly appreciate if we can expedite this.

[kneal]

@mholt Any updates on this one?

[mholt]

Nope, sorry, if there were updates they would be posted here.

I've been busy readying the Caddy 2 release. In the meantime, this PR needs tests, as stated above.

[jbrockopp]

@technicianted @mholt

I've opened a separate PR that attempts to copy the changes made in this PR, but also add tests:

#230

Please let me know if anything else is required 👍

[mholt]

Probably fixed in #296.