[proton repo] Aliasing trunk to master.

[Alan Conway <ac...@redhat.com>]

Can we do something like this in the proton repo please:
 git symbolic-ref refs/heads/trunk refs/heads/master

The switch from trunk to master was confusing - at best time wasted on
"what the...?" moments, at worst some unsuspecting soul will push
changes to trunk and then wonder why they don't show up in a release. It
also played havoc with some automated build systems I am friends with.

Making trunk an alias for master would leave master in charge but not
trip up those who are expecting trunk. 

All the trunk history is on master anyway, we can put a trunk-rip tag to
show where it ended if anybody cares.

Cheers,
Alan.