Handle any null pointer exceptions that might occur when looking for …

…AppleSDKs

Merge remote-tracking branch 'facebook/master'

Ensure maven pom tempalte is built properly

Merge remote-tracking branch 'facebook/master'

Get the selenium build working again

Fix mozilla xpi builds

Better use of output paths

Introduce a build_stamp rule

This will always be executed, leading to uncacheable and
unrepeatable builds. If we were smart, we'd hide this
behind a flag and only do the non-deterministic thing if
that seemed like a Good Idea. At least this way, there's
no danger of us ever forgetting to add the stamp.

Fix problem compiling maven jars

Add back in pgp signing for maven publish

Because we need it