Support coloring console on Windows

Introduce github.com/mattn/go-colorable to solve the console color
issues on Windows

bitbucket.org/kardinaos/osxt was removed and github.com/inconshreveable/go-update has changed to use github.com/kardianos/osext. Not bumping go-update will prevent upgrade of other packages with `godep save -r ./…`

Fix password insertion more than 15 characters on Windows

Bumping to the latest gopass. This fixes https://github.com/github/hub/issues/837.

After `browse` was indicated as "GitExtension: false", it now gets
automatically parsed by pflag library. That has an adverse effect that
it loses information about the `--` value being passed, since pflag
treats it as terminator value and swallows it silently.

Now, introduce the `args.Terminator` property to check if terminator was
present or not, and use that in `browse` to restore previous behavior.

The `browse` command is not an extension to an existing git command.

Fixes #918

Add OSX build to Travis

Faster than `brew install tmux` which depends on openssl package

Travis `cache` directive doesn't seem supported on its osx environment.

This is needed for the osx Travis environment which apparently doesn't
support built-in caching.

This reverts commit 3cba4e5d.

Use `--no-tags` for new remotes in `checkout/cherry-pick`

This is so the tags from the automatically-added remote (typically
someone's fork) don't spill in and mix with the current tags.

fix non-portable GNU find(1)-ism

GNU find(1)'s -not operator is not POSIX compliant.  Use ! operator
instead in order to work with other find(1) implementations.

useHttpProtocol => useProtocol, allow ssh config

`useHttpProtocol` has been changed to a more generic `preferedProtocol`
function that can be used to check the users hub.protocol settings. This
allows us to use the SSH protocol in any location, regardless of the
repository being private or public.

```
% git config --global hub.protocol ssh
% ./hub --noop clone github/hub
git clone git@github.com:github/hub.git
% git config --global hub.protocol https
% ./hub --noop clone github/hub
git clone https://github.com/github/hub.git
% git config --global hub.protocol none
% ./hub --noop clone github/hub
git clone git://github.com/github/hub.git
```

Tests were also added for `HUB_PROTOCOL = ssh`.

- Add test for `pull-request -a`
- Narrow scope of `updateIssue` to `updateIssueAssignee`

Check for empty git config

This fixes #858

Make the ssh config reader case-insensitive

Fixes #831 [ci skip]

Use `.Login` instead of `.Name` for generating a remote or branch name.

It is `headRepo.Owner.Login` that holds the unix account name of the
owner, and `headRepo.Owner.Name` is omitted from the embedded owner
information, resulting in the following failure:

```
% hub checkout https://github.com/github/hub/issues/{number}
fatal: '' is not a valid remote name
```

Avoid using "label" field when parsing PR response

To obtain the owner/fork-name combo, instead of reading it from "label"
field from the PR response simply read from `Head.Ref` and
`Head.Repo.Owner.Name` instead. This is because label is meant to be
human-readable, isn't well-documented in GitHub API docs and is unclear
when it contains two components (delimited by `:`) and when it contains
only one.

Extract logic of printing out to console