NSIS has a default MAX_STR_LEN of 1024. If $ENV{PATH} is longer
the returned string is truncated to an empty string. Its then not
possible to distinguis between the variable not set or too long.
As a result the variable is set with the location where geth and/or
dev tools are installed. This may override any previous set values.

* build: modify the iOS namespace to iGeth (gomobile limitation)
* mobile: assign names to return types for ObjC wrapper
* mobile: use more expanded names for iOS/Swift API

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

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.

archiveUpload did not handle absolute paths correctly. Fix it by using
the basename and ensure that uploads can be tested using -n.

This commit adds support for creating Windows installers to ci.go

* travis.yml: don't create darwin/386 builds

* build: remove godep remains

* internal/build: improve archives

- enable compression for zip files
- don't write half-complete archives

* build: add -unstable to archive names

This commit converts the dependency management from Godeps to the vendor
folder, also switching the tool from godep to trash. Since the upstream tool
lacks a few features proposed via a few PRs, until those PRs are merged in
(if), use github.com/karalabe/trash.

You can update dependencies via trash --update.

All dependencies have been updated to their latest version.

Parts of the build system are reworked to drop old notions of Godeps and
invocation of the go vet command so that it doesn't run against the vendor
folder, as that will just blow up during vetting.

The conversion drops OpenCL (and hence GPU mining support) from ethash and our
codebase. The short reasoning is that there's noone to maintain and having
opencl libs in our deps messes up builds as go install ./... tries to build
them, failing with unsatisfied link errors for the C OpenCL deps.

golang.org/x/net/context is not vendored in. We expect it to be fetched by the
user (i.e. using go get). To keep ci.go builds reproducible the package is
"vendored" in build/_vendor.

This commit tweaks the debian packaging tool:

* All build environment metadata can now be overriden on the command
  line. This allows testing the CI build behaviour locally.
* -unstable packages now actually contain the binaries (oops)
* packages use Go 1.7 to build
* archiving is skipped for PR builds

TravisCI and AppVeyor run the tests in very slow VMs.
Some of our tests can't cope with that. Running less tests
in parallel should make them somewhat less flakey.

The new build script, ci.go, replaces some of the older shell scripts.
ci.go can compile go-ethereum, run the tests, create release archives
and debian source packages.