Fix bug when filtering s3 locations

[jamesls]

The pattern is evaluated against the entire bucket. This doesn't
mattern for suffix searches, but for a prefix search, you'd have to
include the bucket name. This is inconsistent with filtering local
files. Now they're both consistent. Given:

  --exclude 'foo*'

This will filter any full path that startsw with foo. So locally:

  rootdir/
    foo.txt      # yes
    foo1.txt     # yes
    foo/bar.txt  # yes
    bar.txt      # no

And on s3, we now have the same results:

  bucket/
    foo.txt      # yes
    foo1.txt     # yes
    foo/bar.txt  # yes
    bar.txt      # no

I also added debug logs to help customers troubleshoot why their
filters aren't working the way they expect. For example:

s3.filters - DEBUG - /private/tmp/syncme/level-1/file-7 matched exclude filter: /private/tmp/syncme/*
s3.filters - DEBUG - /private/tmp/syncme/level-1/file-7 did not match include filter: /private/tmp/syncme/f*
s3.filters - DEBUG - /private/tmp/syncme/level-1/file-7 matched include filter: /private/tmp/syncme/level*
s3.filters - DEBUG - =/private/tmp/syncme/level-1/file-7 final filtered status, should_include: True

[garnaat]

LGTM