NEXUS-5744: fix for redirect strategy

There was initially a "prevent redirection to index pages"
check that proved to be overly broad. It was meant to prevent
redirections like:

http://host/path -> http://host/path/

as "path" is actually a collection (directory in HTTP lingo)
on server side, and this is usual redirections that HTTP
servers do when asked for that 1st URL.

But, this check was too broad, as it prevented redirections
like

http://hostA/path/ -> http://hostB/path/

for example (same for HTTP -> HTTPS or even port change),
as it was checking only that 2nd URL does not end with slash.
NEXUS-5744: Smaller fix and UT

UT extended to check that index page redirect still
kicks in, but cross site redirects are allowed.
Merge pull request #26 from sonatype/nexus-5744-redirect-strategy-fix

NEXUS-5744: fix for redirect strategy