This reverts commit b6c7b83e.

This reverts commit 4ddeeb84.

Advertise X-JNLP-Host-Name correctly

This allows TCP slave agent port to be reverse proxied.

Signed-off-by: NKamran Mackey <kamranm1200@gmail.com>

BIGNUMBER_STAR mode has been selected, because it utilizes GNU extensions (like LONGFILE_GNU does).

This test also introduces additional round-trip tests for small files

[FIXED JENKINS-27708][FIXED JENKINS-27871]  Ensure that identification of blocked tasks is using the live state.

- The creation of a snapshot itself should be relatively cheap given the expected rate of
  job execution. You probably would need 100's of jobs starting execution every iteration
  of maintain() before this could even start to become an issue and likely the calculation
  of isBuildBlocked(p) will become a bottleneck before updateSnapshot() will. Additionally
  since the snapshot itself only ever has at most one reference originating outside of the stack
  it should remain in the eden space and thus be cheap to GC.

- JENKINS-27708 comments 225819 and 225906 provide more complex but logically equivalent fixes of
  this issue. I am favouring this approach as it is simpler and provides less scope for error as any
  new helper methods can just rely on the snapshot being up to date whereas with the other
  two candidates if a new helper method is introduced there is the potential to miss adding support
  for the live view. The comment 225819 has the risk of introducing extra lock contention while
  the comment 225906 version forces every access to the helper methods to pass a second memory
  barrier

Without this change you need to do:

```
User user;
final SecurityContext oldContext = ACL.impersonate(a);
try {
    user = User.current();
} finally {
    SecurityContextHolder.setContext(oldContext);
}
```

Which seems incredibly wasteful.

Or else you need to replicate the logic in User.current() which makes that code hard to change.

This reverts commit fe1a1487.
It's been about a month, so I think it has served its purpose.

Allowing some methods to be overridden, with the caveat that the overrides will not be called from CoreWrapperStep.