Support Vagrant: quick & easy Linux virtual machine setup

When developing Git for Windows, we always have to ensure that we do not
break any non-Windows platforms, e.g. by introducing Windows-specific code
into the platform-independent source code.

At other times, it is necessary to test whether a bug is Windows-specific
or not, in order to send the bug report to the correct place. Having
access to a Linux-based Git comes in really handy in such a situation.

Vagrant offers a painless way to install and use a defined Linux
development environment on Windows (and other Operating Systems). We offer
a Vagrantfile to that end for two reasons:

1) To allow Windows users to gain the full power of Linux' Git

2) To offer users an easy path to verify that the issue they are about
   to report is really a Windows-specific issue; otherwise they would
   need to report it to git@vger.kernel.org instead.

Using it is easy: Download and install https://www.virtualbox.org/, then
download and install https://www.vagrantup.com/, then direct your
command-line window to the Git source directory containing the Vagrantfile
and run the commands:

	vagrant up
	vagrant ssh

See https://github.com/git-for-windows/git/wiki/Vagrant for details.

As part of switching Git for Windows' development environment from msysGit
to the MSys2-based Git SDK, this Vagrantfile was copy-edited from msysGit:

	https://github.com/msysgit/msysgit/blob/0be8f2208/Vagrantfile

Signed-off-by: Johannes Schindelin <johannes.schindelin@gmx.de>

.gitignore

@@ -269,3 +269,6 @@ Release/
 /UpgradeLog*.htm
 /git.VC.VC.opendb
 /git.VC.db
+/.vagrant/
+/vagrant2[0-9][0-9][0-9]*-*-*
+/d2[0-9][0-9][0-9]*-*-*

Vagrantfile

@@ -0,0 +1,57 @@
+# -*- mode: ruby -*-
+# vi: set ft=ruby :
+
+# This Vagrantfile defines the requirements of a Linux development environment
+# to develop/run Git. This environment can be set up conveniently by installing
+# Vagrant and VirtualBox and calling "vagrant up" in the /usr/src/git directory.
+#
+# See https://github.com/git-for-windows/git/wiki/Vagrant for details.
+
+# Vagrantfile API/syntax version. Don't touch unless you know what you're doing!
+VAGRANTFILE_API_VERSION = "2"
+
+$provision = <<PROVISION
+apt-get update
+apt-get install -y make gcc libexpat-dev libcurl4-openssl-dev gettext tk8.6 libsvn-perl
+
+# clean .profile in case we're re-provisioning
+n="$(grep -n 'cd /vagrant' < /home/vagrant/.profile 2> /dev/null |
+	sed 's/:.*//')"
+test -z "$n" || {
+	head -n $(($n-1)) < /home/vagrant/.profile > /tmp/.profile
+	mv /tmp/.profile /home/vagrant/.profile
+}
+
+# add a nice greeting
+cat >> /home/vagrant/.profile << \EOF
+
+cd /vagrant/
+export PATH=/home/vagrant/bin:$PATH
+cat << \TOOEOF
+
+Welcome to the Vagrant setup for Git!
+--------------------------------------
+
+To build & install Git, just execute
+
+	make -j NO_PERL_MAKEMAKER=t install
+
+For more information, see https://github.com/git-for-windows/git/wiki/Vagrant
+TOOEOF
+EOF
+
+cat << EOF
+
+Now that everything is set up, connect to the Vagrant machine with the command:
+
+	vagrant ssh
+
+EOF
+PROVISION
+
+Vagrant.configure(VAGRANTFILE_API_VERSION) do |config|
+  config.vm.box = "ubuntu/trusty64"
+  config.vm.box_url = "https://atlas.hashicorp.com/ubuntu/boxes/trusty64"
+
+  config.vm.provision :shell, :inline => $provision
+end