Add support for control of the timeouts for XrdAdaptor.
Be more aggressive about retrying on an invalid response.
Wait until any outstanding file-opens finish before deleting underlying
resources.

Additionally, make a number of improvements in the initial file-open
and error messages in the event of a failure.
Improve the retry handler for file-opens.
Merge pull request #3491 from bbockelm/multisource_xrootd_v4

xrootd -- Multisource xrootd v4
Small fixes for timeouts and error messages.
Add recovered file handle to the list of active sources.
Merge pull request #3538 from bbockelm/multisource-bugfixes

Multisource bugfixes
Allow both IPv4 and IPv6 addresses to be used.
Add support for sending monitoring info.
Merge pull request #3625 from bbockelm/multisource-bugfixes-v2

Re-add missing features in multisource code