Speed up unpack_file_url
Speed up unpack_file_url

E.g.: `pip install /path/to/dir`

by building an sdist and then unpacking it instead of doing
`shutil.copytree`. `shutil.copytree` may copy files that aren't included
in the sdist, which means that:

1. If those files are large, a `pip install` could take much longer than
it should.

2. Folks that are using `python setup.py install` to test their package
are not fully testing it, because it may copy over files that wouldn't
be there if they built and sdist and installed that.

So this method building an sdist is both more accurate and faster.

Fixes https://github.com/pypa/pip/issues/2195

benesch/pip,h4ck3rm1k3/pip,sbidoul/pip,xavfernandez/pip,wkeyword/pip,tdsmith/pip,zenlambda/pip,techtonik/pip,sigmavirus24/pip,wkeyword/pip,fiber-space/pip,willingc/pip,prasaianooz/pip,mujiansu/pip,rouge8/pip,jasonkying/pip,pradyunsg/pip,fiber-space/pip,mujiansu/pip,davidovich/pip,supriyantomaftuh/pip,zenlambda/pip,mindw/pip,chaoallsome/pip,dstufft/pip,pfmoore/pip,ncoghlan/pip,luzfcb/pip,atdaemon/pip,RonnyPfannschmidt/pip,yati-sagade/pip,davidovich/pip,supriyantomaftuh/pip,pypa/pip,haridsv/pip,prasaianooz/pip,graingert/pip,rbtcollins/pip,davidovich/pip,zvezdan/pip,habnabit/pip,h4ck3rm1k3/pip,erikrose/pip,harrisonfeng/pip,KarelJakubec/pip,zenlambda/pip,qbdsoft/pip,habnabit/pip,esc/pip,dstufft/pip,James-Firth/pip,caosmo/pip,zorosteven/pip,RonnyPfannschmidt/pip,wkeyword/pip,mindw/pip,sbidoul/pip,blarghmatey/pip,yati-sagade/pip,pradyunsg/pip,erikrose/pip,jmagnusson/pip,Gabriel439/pip,habnabit/pip,xavfernandez/pip,nthall/pip,KarelJakubec/pip,erikrose/pip,pfmoore/pip,Gabriel439/pip,sigmavirus24/pip,pypa/pip,squidsoup/pip,qbdsoft/pip,supriyantomaftuh/pip,natefoo/pip,esc/pip,squidsoup/pip,jythontools/pip,chaoallsome/pip,luzfcb/pip,jasonkying/pip,rouge8/pip,zorosteven/pip,jmagnusson/pip,caosmo/pip,dstufft/pip,ncoghlan/pip,prasaianooz/pip,natefoo/pip,natefoo/pip,Gabriel439/pip,techtonik/pip,zorosteven/pip,chaoallsome/pip,haridsv/pip,benesch/pip,sigmavirus24/pip,ncoghlan/pip,ChristopherHogan/pip,atdaemon/pip,blarghmatey/pip,rbtcollins/pip,caosmo/pip,atdaemon/pip,alex/pip,alex/pip,tdsmith/pip,mujiansu/pip,esc/pip,jamezpolley/pip,luzfcb/pip,harrisonfeng/pip,fiber-space/pip,haridsv/pip,jythontools/pip,xavfernandez/pip,mindw/pip,RonnyPfannschmidt/pip,jasonkying/pip,jamezpolley/pip,harrisonfeng/pip,rouge8/pip,KarelJakubec/pip,alex/pip,willingc/pip,benesch/pip,ChristopherHogan/pip,jythontools/pip,nthall/pip,James-Firth/pip,jamezpolley/pip,zvezdan/pip,graingert/pip,graingert/pip,techtonik/pip,squidsoup/pip,willingc/pip,nthall/pip,yati-sagade/pip,jmagnusson/pip,zvezdan/pip,rbtcollins/pip,James-Firth/pip,qbdsoft/pip,tdsmith/pip,ChristopherHogan/pip,h4ck3rm1k3/pip,blarghmatey/pip