NEXUS-5838: RRB uses wrong path in case of some index pages.

Code was prepared for two possibilities: that "A" tag "HREF"
attribute contains relative paths (taken from index page base),
or, that "HREF" attribute contains full URLs.

But here we have a third case: the "HREF" attribute contains
absolute paths from the server root.

Hence, the paths were wrongly assembled, as the basePath
element was duplicated in the URL requested from remote.
Merge pull request #132 from sonatype/nexus-5838-rrb-wrong-path

NEXUS-5838: RRB uses wrong path in case of some index pages