Force the use of Fabric 1.4

Fabric 1.7 causes errors like:

	Requested: git clone -b master chris@gcc.flexdns.net:mailer /var/django/mailer/dev
	Executed: sudo -S -p 'sudo password:'  /bin/bash -l -c "cd /var/django/mailer && PATH=\$PATH:\"<module 'posixpath' from '/home/installuser/projects/mailer/django/website/.ve/lib/python2.7/posixpath.pyc'>\" git clone -b master chris@gcc.flexdns.net:mailer /var/django/mailer/dev"

Probably because env.path is no longer a list, but a `posixpath` object:

	672  ->	    env_vars = {}
	673
	674  	    # path(): local shell env var update, appending/prepending/replacing $PATH
	675  	    path = env.path
	676  	    if path:
	677  	        if env.path_behavior == 'append':
	(Pdb) n
	> /home/installuser/projects/mailer/django/website/.ve/lib/python2.7/site-packages/fabric/operations.py(675)_prefix_env_vars()
	-> path = env.path
	(Pdb) p env.path
	<module 'posixpath' from '/home/installuser/projects/mailer/django/website/.ve/lib/python2.7/posixpath.pyc'>
	(Pdb) q
	Traceback (most recent call last):
	  File "/home/installuser/projects/mailer/django/website/.ve/lib/python2.7/site-packages/fabric/main.py", line 743, in main
	    *args, **kwargs
	  File "/home/installuser/projects/mailer/django/website/.ve/lib/python2.7/site-packages/fabric/tasks.py", line 368, in execute
	    multiprocessing
	  File "/home/installuser/projects/mailer/django/website/.ve/lib/python2.7/site-packages/fabric/tasks.py", line 264, in _execute
	    return task.run(*args, **kwargs)
	  File "/home/installuser/projects/mailer/django/website/.ve/lib/python2.7/site-packages/fabric/tasks.py", line 171, in run
	    return self.wrapped(*args, **kwargs)
	  File "/home/installuser/projects/mailer/django/website/.ve/src/dye/dye/fablib.py", line 146, in deploy
	    _create_dir_if_not_exists(env.server_project_home)
	  File "/home/installuser/projects/mailer/django/website/.ve/src/dye/dye/fablib.py", line 131, in _create_dir_if_not_exists
	    sudo_or_run('mkdir -p %s' % path)
	  File "/home/installuser/projects/mailer/django/website/.ve/src/dye/dye/fablib.py", line 496, in sudo_or_run
	    return sudo(command)
	  File "/home/installuser/projects/mailer/django/website/.ve/lib/python2.7/site-packages/fabric/network.py", line 578, in host_prompting_wrapper
	    return func(*args, **kwargs)
	  File "/home/installuser/projects/mailer/django/website/.ve/lib/python2.7/site-packages/fabric/operations.py", line 1095, in sudo
	    stderr=stderr, timeout=timeout, shell_escape=shell_escape,
	  File "/home/installuser/projects/mailer/django/website/.ve/lib/python2.7/site-packages/fabric/operations.py", line 895, in _run_command
	    _prefix_commands(_prefix_env_vars(command), 'remote'),
	  File "/home/installuser/projects/mailer/django/website/.ve/lib/python2.7/site-packages/fabric/operations.py", line 675, in _prefix_env_vars
	    path = env.path
	  File "/home/installuser/projects/mailer/django/website/.ve/lib/python2.7/site-packages/fabric/operations.py", line 675, in _prefix_env_vars
	    path = env.path