Fixes from debugging relval 4.22
- Fix opaque string to not include two '?'.
- Break up large readv requests into smaller pieces, within the
  Xrootd server limits.
- Correctly throw an exception on error.
- Tidy up some exception messages to not lose original error.
- Avoid an infinite loop if the Xrootd redirector ignores our
  request to avoid servers.
- Merge adjacent requests when splitting the input vector.
Avoid negative values for consumed.
Next attempt at the new xrootd code

Revert "Revert "Merge pull request #558 from bbockelm/multisource-xrootd""

This reverts commit d0a3832bf1bcaed3f2c358b4807cac0f1060d94f.
Merged multisource-xrootd-fixes from repository bbockelm
Remove final pieces of old XrdClient.
Fixes from debugging relval failures:
Add more validation to the readv chunks.
Avoid calling ML from a multithreaded context.
Avoid reordering locks.
Retry if the server sends an invalid response.
Merge pull request #2575 from nclopezo/multisource-xrootd-v3

xrootd -- Multisource xrootd v3
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.
Allow both IPv4 and IPv6 addresses to be used.
Add support for sending monitoring info.
Merge branch 'from-CMSSW_7_2_0_pre1' into multisource-bugfixes-v3

Conflicts:
	IOPool/Input/src/RootInputFileSequence.cc
	Utilities/XrdAdaptor/src/XrdFile.cc
multi-thread safe porting
Function storeBadEvents removed
local storage of the ibooker and igetter pointers in clients removed
conflicts fixed
renaming of sequence from Validation to DQM