Rework IndexScanPlan costing to favor filtering indexes over for-ordering-only indexes.
Merge branch 'ENG-4079' into ENG-4077

Conflicts:
	tests/frontend/org/voltdb/planner/TestDeterminism.java
Allow EE build overrides, e.g. clang instead of gcc.
Merge branch 'master' into ENG-4077
Merge branch 'master' into ENG-4077
Favor index-for-filtering over index-for-sort in more cases by tweaking IndexScan cost and eliminating redundant Send cost.
Merge branch 'master' into ENG-4077
ENG-4077 Final? explain and estimate (lower) LT/LTE index scans differently from order-only scans.
Add plannertester test suite: ENG-4077-prefer-filtering-index
txnid2: change needed for apprunner recovery checks:
    write txnCount to disk once per second.
Merge pull request #361 from VoltDB/ENG-4077

Review-ready -- pull should wait for new plannertester test case for automated validation.
Set return_code on exception exits.
Merge pull request #369 from VoltDB/ENG-4289

Allow EE build overrides, e.g. clang instead of gcc.
ENG-3153, ENG-3154, ENG-3163: Bug fix and test cleanup.
Seems to work now.
Disabled some broken export tests (need to be fixed before merge).
Merge remote-tracking branch 'origin/master' into ENG-3153-liveschema