Prepare v28r2

See merge request !307

Sequential scheduling of an algorithm set (native support)

See merge request !305

needed with ROOT and LCG 88

Hide new proprty "Atomic" in tests

See merge request !301

fixed compilation with Clang

See merge request !294

See merge request !299

See merge request !304

allow the new scheduler-based mechanism of algorithms sequencing be controlled by AthSequencer property 'Sequential'

migrate from the concept of 'laziness', inherited from the era of GaudiSequencers', to a more meanignful concept of a 'prompt decision' (the change affected the PrecedenceRulesGraph only)

rename the root decision hub of the graph of precedence rules from 'EVENT LOOP' to 'RootDecisionHub'.

 o add explicit typing of a decision hub node as parallel/sequential (before it was considered as parallel by default, could be made 'sequential' with few dirty tricks);
 o make precedence graph traversals respect the parallel/sequential flag;
 o I also took this occasion to re-factor the bottom-up part of CF graph traversal making it based on graph visitor pattern instead of recursive one.

changed default LCG version to 88

See merge request !303

Closes GAUDI-1293

See merge request !296

See merge request !300

the property was added with !287

DataHandle: add flag to identify Conditions

See merge request !293

Add AvalancheSchedulerSvc and clean up the ForwardSchedulerSvc

See merge request !288

Make sure that entries in m_flatUniqueAlgList are actually unique

See merge request !255

Conflicts:
	GaudiHive/src/AlgResourcePool.cpp

Fix HistoStats in GaudiUtils to prevent floating point exceptions due to 'bad' return values

See merge request !270

allow multiple handlers for a protocol in VFSSvc

See merge request !295

Support for AthSequencers in Scheduler

See merge request !287

- use new Gaudi::Property
- changes to work as ForwardSchedulerSvc DataLoaderAlg (!269)

Attribute unmet INPUT dependencies to a DataLoader Algorithm

See merge request !269

See merge request !79

Closes GAUDI-1276

See merge request !267

fixes to CMake modules

Closes LBCORE-1304

See merge request !298

Closes LBCORE-1228

See merge request !289

gdb can be found in /usr/bin, in which case its directory must
not be prepended to the custom PATH