Newer cleaner shell tests based on roundup (https://github.com/bmizerany/roundup)

Newer cleaner shell tests based on roundup (https://github.com/bmizerany/roundup)

```
~/dev/git-repos/virtualenv/tests/shell$ make
./roundup *-test.sh
virtualenv
  it_displays_usage:                               [PASS]
  it_creates_a_virtualenv:                         [PASS]
  it_sets_VIRTUAL_ENV:                             [PASS]
  it_creates_directories:                          [PASS]
  it_picks_up_right_python:                        [PASS]
  it_picks_up_right_pip:                           [PASS]
  it_picks_up_right_easy_install:                  [PASS]
  it_populate_sys_executable_correctly:            [PASS]
  it_can_run_pydoc_on_a_module_in_the_virtualenv:  [PASS]
  it_creates_deactivate_function:                  [PASS]
  it_can_deactivate:                               [PASS]
=========================================================
Tests:   11 | Passed:  11 | Failed:   0
```