WIP: Refactor for History enumeration and ObjectStreamHandler

[idodeclare]

@vladak , see:

• HistoryEnumeration
• FileHistoryTemp that uses HaloDB, and revising FileHistoryCache's to use FileHistoryTemp
• ObjectStreamHandler and revising Executor to support it
• GitHistoryParser revised as an ObjectStreamHandler
• SingleHistory implementation for all other repositories which I did not convert to be ObjectStreamHandler.

[coveralls]

Pull Request Test Coverage Report for Build 5468

• 603 of 780 (77.31%) changed or added relevant lines in 38 files are covered.
• 38 unchanged lines in 15 files lost coverage.
• Overall coverage increased (+0.05%) to 75.767%

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Changes Missing Coverage	Covered Lines	Changed/Added Lines	%
opengrok-indexer/src/main/java/org/opengrok/indexer/history/AccuRevRepository.java	0	1	0.0%
opengrok-indexer/src/main/java/org/opengrok/indexer/history/BazaarTagEntry.java	0	1	0.0%
opengrok-indexer/src/main/java/org/opengrok/indexer/history/ClearCaseRepository.java	0	1	0.0%
opengrok-indexer/src/main/java/org/opengrok/indexer/history/GitRepository.java	13	14	92.86%
opengrok-indexer/src/main/java/org/opengrok/indexer/history/MonotoneRepository.java	0	1	0.0%
opengrok-indexer/src/main/java/org/opengrok/indexer/history/RCSRepository.java	1	2	50.0%
opengrok-indexer/src/main/java/org/opengrok/indexer/history/SSCMRepository.java	0	1	0.0%
opengrok-indexer/src/main/java/org/opengrok/indexer/index/IndexDatabase.java	0	1	0.0%
opengrok-indexer/src/main/java/org/opengrok/indexer/history/MonotoneHistoryParser.java	0	2	0.0%
opengrok-indexer/src/main/java/org/opengrok/indexer/history/PerforceRepository.java	0	2	0.0%

Files with Coverage Reduction	New Missed Lines	%
opengrok-indexer/src/main/java/org/opengrok/indexer/analysis/plain/PlainAnalyzerFactory.java	1	95.24%
opengrok-indexer/src/main/java/org/opengrok/indexer/history/Repository.java	1	81.21%
opengrok-indexer/src/main/java/org/opengrok/indexer/index/IndexDatabase.java	1	60.21%
opengrok-indexer/src/main/java/org/opengrok/indexer/web/Util.java	1	66.06%
opengrok-indexer/src/main/java/org/opengrok/indexer/configuration/IndexTimestamp.java	2	42.86%
opengrok-indexer/src/main/java/org/opengrok/indexer/history/MonotoneHistoryParser.java	2	0%
opengrok-indexer/target/generated-sources/jflex/org/opengrok/indexer/analysis/document/TroffFullTokenizer.java	2	80.25%
opengrok-indexer/target/generated-sources/jflex/org/opengrok/indexer/analysis/document/TroffXref.java	2	76.25%
opengrok-indexer/target/generated-sources/jflex/org/opengrok/indexer/analysis/erlang/ErlangSymbolTokenizer.java	2	73.62%
opengrok-indexer/target/generated-sources/jflex/org/opengrok/indexer/analysis/fortran/FortranSymbolTokenizer.java	2	82.52%

Totals
Change from base Build 5462:	0.05%
Covered Lines:	41706
Relevant Lines:	55045

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💛 - Coveralls