[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