(cherry picked from commit 0bd831e2)

(cherry picked from commit 747d550c)

(cherry picked from commit 9259f873)

(cherry picked from commit 071951e6)

(cherry picked from commit b628b472)

(cherry picked from commit 04aace98)

(cherry picked from commit e4ba41d5)

(cherry picked from commit 5d9e4d7b)

(cherry picked from commit b9d8f554)

(cherry picked from commit 42195d83)

(cherry picked from commit dbed3044)

Conflicts:
	core/src/main/java/hudson/model/Run.java

(cherry picked from commit d72fda46)

(cherry picked from commit e405078e)

(cherry picked from commit 4aad749c)

Conflicts:
	core/src/main/java/hudson/matrix/MatrixBuild.java
	core/src/main/java/hudson/matrix/MatrixConfiguration.java
	core/src/main/java/hudson/matrix/MatrixProject.java
	core/src/main/resources/hudson/matrix/MatrixProject/configure-entries.jelly

[SECURITY-163] Non-browser-based DownloadService

In 20340e18 @daniel-beck suggested updating this text.

Avoids rechecking at every startup, mainly relevant during interactive testing when restarts may be quite frequent.

In this case we are probably interested in looking at the output as it arrives in real time.
Can always be overridden on the command line if desired.
(cherry picked from commit 44a8ec11)

Also moving this switch to security settings.

(cherry picked from commit 6318b8d8)

(cherry picked from commit e4c5c710)

(cherry picked from commit df9c92e4)

(cherry picked from commit 1c99cc1a)

loadJSON does not support parsing HTML.
Nor should it need to, since UC URLs are supposed to be to the JSONP file.
The .html extension is added automatically by downloadService when postBack is supported.
(cherry picked from commit d6b37a94)

Conflicts:
	test/src/test/java/hudson/model/UpdateSiteTest.java
	test/src/test/resources/hudson/model/update-center.json.html

(cherry picked from commit fb524145)

@kohsuke prefers that the option to disable signature checks not even be presented unless -Dhudson.model.DownloadService.noSignatureCheck is used.
(cherry picked from commit 54c85007)

Be a bit paranoid and ensure the admin has CONFIGURE_UPDATECENTER before turning off signature checks.

(cherry picked from commit 1262d882)

(cherry picked from commit 1ac77750)

Conflicts:
	core/src/main/java/hudson/model/DownloadService.java
	core/src/main/java/hudson/model/UpdateSite.java