Go component

Add support for Go language in the form of providing component for Go
toolchain and stdlib.

Current Go stable series is 1.5.* but to bootstrap it one need to have
Go 1.4.* available, which itself needs C compiler to bootstrap.

We need Go support for upcoming GitLab SR, where one server is written
in this language:

    https://gitlab.com/gitlab-org/gitlab-workhorse

/cc @gabriel, @Camata

component/golang/buildout.cfg

+# Go language - https://golang.org/
+[buildout]
+parts = golang
+
+[golang]
+<= golang15
+
+
+[golang-common]
+recipe = slapos.recipe.cmmi
+configure-command = :
+location = ${buildout:parts-directory}/${:_buildout_section_name_}
+make-binary =
+make-targets= cd src && ./all.bash && cp -alf .. ${:location}
+environment =
+  GOROOT_FINAL=${:location}
+  ${:environment-extra}
+
+
+[golang14]
+<= golang-common
+url = https://storage.googleapis.com/golang/go1.4.3.src.tar.gz
+md5sum = dfb604511115dd402a77a553a5923a04
+environment-extra =
+
+
+[golang15]
+<= golang-common
+url = https://storage.googleapis.com/golang/go1.5.1.src.tar.gz
+md5sum = 4adfbdfca523cc1c229be8a321f3602f
+
+# go1.5 needs go1.4 to bootstrap
+environment-extra =
+  GOROOT_BOOTSTRAP=${golang14:location}