[FIXED JENKINS-19945] Upgraded bundled plugin versions

(cherry picked from commit 2f846ea9a0c0714402c248c103b1d10c7fdb101f)

Conflicts:
	changelog.html
[JENKINS-19192] Using JNR 3.0.1 which includes JNR-FFI 1.0.7; 1.0.6 has the backported fix for Guava #1505, the root cause.
So this upgrade ought to prevent a recurrence of the issue in case some other code refers to JNR from the CLI.
(As yet untested, and we do not especially want to send JNR over the CLI channel anyway for performance reasons.)

(cherry picked from commit 53ce4f0fa74bc2c71cd249635452ade2c7118256)
[FIXED JENKINS-10675] use X-Forwarded-Proto if present

(cherry picked from commit ddfa65fae64663cda51a7b9dd7b45eeebbd10eda)
[fixed JENKINS-19740] Added postCheckout for SCMs

(cherry picked from commit e4ba0b365986b1da7c04c881b5edf33df3c4f826)
maven plugin is moved off to a separate repository.

See https://github.com/jenkinsci/maven-plugin

(cherry picked from commit f98070d3e6dabab0817f80f2526f78f61ffa1c83)

Conflicts:
	maven-plugin/pom.xml
	maven-plugin/src/main/java/hudson/maven/MavenModuleSetBuild.java
	maven-plugin/src/main/resources/hudson/maven/MavenModuleSet/configure-entries.jelly
	plugins/pom.xml
Updated to maven-plugin 2.0 general release.

(cherry picked from commit 9b53643c7a573f64fe199ca8c9f5b60d8a3d771f)
[FIXED JENKINS-18836][FIXED JENKINS-18879][FIXED JENKINS-19619] Upgrade trilead-ssh to version with the fix

(cherry picked from commit bb265c5e95b0fe39128720b903914236962db41b)

Conflicts:
	changelog.html
[FIXED JENKINS-20085] Overflow in Jenkins.globalIota. Simpler and safer to use an AtomicLong.

(cherry picked from commit 587c6fe317bfe3560069ceb41495c6f5f5d114d1)

Conflicts:
	changelog.html
[FIXED JENKINS-20071] Upgrade bundled versions of credentials and ssh-slaves so we can assume <c:select/> available

(cherry picked from commit 58af1d629a8b1eb9c088b15621b35a22cd770663)

Conflicts:
	changelog.html
[FIXED JENKINS-19947] Restore historical undocumented behavior of a top-level entry in a ZIP.
Noting that various DirScanner implementations handle this inconsistently.

(cherry picked from commit 793b6826e567e20a256a6d4166031e75a185ef7a)

Conflicts:
	changelog.html
[FIXED JENKINS-18633] Simplified distinction between Jenkins.description and View.description.
Both are shown if defined. The edit description link only applies to View.description.
Properly handle a ViewGroup other than Jenkins itself, such as a folder.
(cherry picked from commit 04c8a1efc0f6324868638be9a4cfdb085e17744f)

Conflicts:
	changelog.html