gitignore: use absolute path

The current content of `.gitignore` is using relative paths. For
example, `test/config.log` would be ignored while it doesn't seem to be
the intent. Use absolute paths. They are still relative to the root of
the repository.
gitignore: add `test-driver` and `compile`

Those are generated by latest versions of autotools.
url: handle scheme omission

When the scheme is omitted in URL overriding (for example `example.com`
instead of `https://example.com`), s3fs is modifying the URL by
inserting `s3.` in the middle of the name  (`examples3..com`).

This can be a bit difficult to troubleshoot and curl seems to handle
schema-less requests just fine. So, just handle this case correctly.
Merge pull request #73 from vincentbernat/fix/git-ignore

Small gitignore fixes
Merge pull request #74 from vincentbernat/fix/url-may-omit-scheme

url: handle scheme omission