invoke ServiceLoader.load() inside of a privileged block

[istudens]

When running with Security Manager enabled in the application server for example, the ObjectMapper fails to read jackson-datatype-jdk8.jar file due to insufficient java.io.FilePermission.

As jackson-databind stands as a library there, it would be nice if ServiceLoader might be called within doPrivileged() method and customers don't need to put additional permissions on their deployments in order to read content of library jar files.

[cowtowncoder]

Thank you for contributing this! I don't know much about this area but I trust this helps in described scenario.

One quick question: does this require any Java 8 features? Baseline for 2.9 is still Java 7.

Aside from this (I assume it is Java 7 safe), all I would need is CLA, usually:

https://github.com/FasterXML/jackson/blob/master/contributor-agreement.pdf

(or, sometimes, Corporate-CLA, also in that repo -- but most devs use individual one)
This is only need before the first contribution.
Easiest way is often to print, fill & sign, scan, email to info at fasterxml dot com.

If you could do that, I'll be happy to merge the PR and it will make it in 2.9.0.pr3.

[istudens]

@cowtowncoder I've finally sent a signed CLA to the email address you mentioned. Thanks.

This PR doesn't use any JDK 8 features.