Introducing the findInPath() method and a test.
We need to use the slave's path separator.
Add work-around for JRE bug, fixes JENKINS-18822.

A nice side-effect is the absolute path to the [default] rake executable
that was used will now be logged.
Fixed PATH tampering to use agent's separator.

File.pathSeparator is incorrect if master and slave are different OS.
Bump parent POM version.

According to Oliver Giles in a Jenkins wiki page comment, a newer JDK
requires a newer version of org.jenkins-ci.plugins:
https://wiki.jenkins-ci.org/display/JENKINS/Plugin+tutorial?focusedCommentId=58002463#comment-58002463
According to Stephen Connolly in the jenkinsci-dev mailing list, 1.447
is a reasonable minimum version to use:
https://groups.google.com/d/msg/jenkinsci-dev/NQTVqUlWu1A/216FyBqycEgJ
Merge pull request #13 from olivierdagenais/JENKINS-18822

Fix JENKINS-18822