Update JGit to 60b81c5a9280e44fa48d533a61f915382b2b9ce2
Update JGit to 60b81c5a9280e44fa48d533a61f915382b2b9ce2

This upgrade provides:
 60b81c5a9 Fix RevWalk.getMergedInto() ignores annotated tags
 c5b305473 Optimize RevWalk.getMergedInto()
 847077151 GitServlet: allow to override default error handlers
 35eeab41b RevWalk: getMergedInto's result is wrong on the second call
 6cb39d145 [test] Create keystore with the keytool of the running JDK
 24d6d6053 Retry loose object read upon "Stale file handle" exception
 12f39c26b Ignore missing javadoc in test bundles
 64b0dee98 Fix garbage collection failing to delete pack file
 ae081b8dc ReachabilityCheckerTestCase: fix reachable from self test case
 1cbfea9ec Prepare 5.13.0-SNAPSHOT builds
 64d0aaa2b Teach independent negotiation (no pack file) using an option "wait-for-done"
 f6b9b392e Fixing visibility for HostEntry constructors.
 a14bc9bb6 Clarify operator precedence to fix errorprone error

Change-Id: I05a330de2bf81d9c51768ea1c1a9d68b67cea48c

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