support PortableGit(msysgit)

fix below.

* git-extras

```
$ git extras
C:\PortableGit\bin\git-extras: line 28: man: command not found
fatal: 'extras' appears to be a git command, but we were not
able to execute it. Maybe git-extras is broken?
```

* git-changelog

```
$ git changelog
mv: cannot move `/tmp/changelog' to `History.md'
```

* git-info

```
$ git info

## Remote URLs:\n
origin  git@github.com:southly/git-extras.git (fetch)
origin  git@github.com:southly/git-extras.git (push)\n
## Remote Branches:\n
:
:
```

* git-alias

```
$ git alias
C:\PortableGit\bin\git-alias: line 4: colrm: command not found
```