use mixin to add 'is git repo' check for some commands

When those commands are used outside a git repo, 'Not a git repo!' will be
printed to stderr
Merge pull request #258 from spacewander/master

use mixin to add 'is git repo' check.
import changes *from* a branch
Merge pull request #260 from brandondrew/patch-1

typo fix.
FIX: representation of git-info

- fix representation of `git-info` output

$ git info --no-config

Before:

 ## Remote URLs:\n
 origin	https://github.com/sanusart/git-extras.git (fetch)
 origin	https://github.com/sanusart/git-extras.git (push)
 upstream	https://github.com/visionmedia/git-extras.git (fetch)
 upstream	https://github.com/visionmedia/git-extras.git (push)\n
 ## Remote Branches:\n
   origin/HEAD -> origin/master
   origin/fix_feature_refactor_bug
   origin/gh-pages
   origin/issue234
   origin/master
   origin/patch-1
   upstream/gh-pages
   upstream/master\n
 ## Local Branches:\n
 * master\n
 ## Most Recent Commit:\n
 commit ac18bd16b4f41cbb5185c42d3d10e0cc39b37e27
 Merge: 68455cf a1b7120
 Author: hemanth.hm <hemanth.hm@gmail.com>

     Merge pull request #260 from brandondrew/patch-1\n
 Type 'git log' for more commits, or 'git show <commit id>' for full commit details.\n

After:

git info --no-config

## Remote URLs:

origin	https://github.com/sanusart/git-extras.git (fetch)
origin	https://github.com/sanusart/git-extras.git (push)
upstream	https://github.com/visionmedia/git-extras.git (fetch)
upstream	https://github.com/visionmedia/git-extras.git (push)

## Remote Branches:

  origin/HEAD -> origin/master
  origin/fix_feature_refactor_bug
  origin/gh-pages
  origin/issue234
  origin/master
  origin/patch-1
  upstream/gh-pages
  upstream/master

## Local Branches:

* master

## Most Recent Commit:

commit ac18bd16b4f41cbb5185c42d3d10e0cc39b37e27
Merge: 68455cf a1b7120
Author: hemanth.hm <hemanth.hm@gmail.com>

    Merge pull request #260 from brandondrew/patch-1

Type 'git log' for more commits, or 'git show <commit id>' for full commit details.