build, internal/build: simplify unstable build checks

I didn't add this initially because the command I tried was too slow.
The 'git for-each-ref ...' invocation takes 40ms on my machine. That
ought to be acceptable.

build: remove hash metadata from cocoapod version

All account's nonce start at 0.

* build: use metatags on cocoapods, not prerelease tags
* build: fix Maven and CocoaPods author email addresses

This simplifies the build and should speed it up a bit because the
standard library doesn't need to be cross compiled on the 32bit builder.

Changed http:// to https:// on one link in README.md

ci.go decides whether a build is unstable by looking at the branch and
tag. This causes issues when a GitHub release is created on the master
branch because the build is considered unstable (the CI environment
reports the branch as "master").

Fix this by looking at the tag only. Any tagged build is stable.

utils: bump stable 1.5.1

build: set GO15VENDOREXPERIMENT in env.sh

This should fix the 'make' build with Go 1.5.

les: fixed logging

Dockerfile revamp

The jit config options are not handled, but random selection still took
place, printing confusing messages.

README, VERSION: update for 1.5 release

utils: unstable 1.5.1

utils: stable 1.5.0

build: master is unstable

travis.yml: upload to the real PPA