Would that finally resolve the issue that an pre-build step error in SCM prevents the job from sending a mail, which explains that the job failed because of SCM, as opposed to now, where there is no notification ?

This addition will not directly solve that issue, but it will allow SCM implementers to circumvent the fact that the creation of workspace, creation of changelog and deliver/merge is done in the same scope.

Code changed in jenkins
User: Christian Wolfgang
Path:
core/src/main/java/hudson/model/AbstractBuild.java
core/src/main/java/hudson/scm/SCM.java
http://jenkins-ci.org/commit/jenkins/e4ba0b365986b1da7c04c881b5edf33df3c4f826
Log:
[fixed JENKINS-19740] Added postCheckout for SCMs

Code changed in jenkins
User: Vojtěch Juránek
Path:
core/src/main/java/hudson/model/AbstractBuild.java
core/src/main/java/hudson/scm/SCM.java
http://jenkins-ci.org/commit/jenkins/4d352aba6e6fd35e516428a2b9f3fe53dcfb3f6c
Log:
Merge pull request #952 from wolfgarnet/master

[fixed JENKINS-19740] Added postCheckout for SCMs

Compare: https://github.com/jenkinsci/jenkins/compare/69ba2b8d6725...4d352aba6e6f

Integrated in jenkins_main_trunk #2903
[fixed JENKINS-19740] Added postCheckout for SCMs (Revision e4ba0b365986b1da7c04c881b5edf33df3c4f826)

Result = SUCCESS
Christian Wolfgang : e4ba0b365986b1da7c04c881b5edf33df3c4f826
Files :

• core/src/main/java/hudson/scm/SCM.java
• core/src/main/java/hudson/model/AbstractBuild.java

Code changed in jenkins
User: Christian Wolfgang
Path:
core/src/main/java/hudson/model/AbstractBuild.java
core/src/main/java/hudson/scm/SCM.java
http://jenkins-ci.org/commit/jenkins/8b8aea6cbe62f120cf296316864dff0f603b6534
Log:
[fixed JENKINS-19740] Added postCheckout for SCMs

(cherry picked from commit e4ba0b365986b1da7c04c881b5edf33df3c4f826)