Allow the metadata to be dumped, use "metadata:" consistently as the public URI for the metadata.

refs #1021
Simplify URI handling in utilities: accept most things the user provides, let the API tell us if it is invalid.

refs #1021
Change WT_METADATA_URI to "metadata:".
Merge pull request #1026 from wiredtiger/metadata-cleanup

Metadata cleanup
Merge pull request #1025 from wiredtiger/dump-metadata

Allow the metadata to be dumped, use "metadata:" consistently