Junction don't copy

Copying the files on windows is very slow and can be avoided by using junctions

Author: blackmamo

lib/pip.js

@@ -610,10 +610,9 @@ function installAllRequirements() {
       !fse.existsSync(symlinkPath) &&
       reqsInstalledAt != symlinkPath
     ) {
-      // Windows can't symlink so we have to copy on Windows,
-      // it's not as fast, but at least it works
+      // Windows can't symlink so we have to use junction on Windows
       if (process.platform == 'win32') {
-        fse.copySync(reqsInstalledAt, symlinkPath);
+        fse.symlink(reqsInstalledAt, symlinkPath, 'junction');
       } else {
         fse.symlink(reqsInstalledAt, symlinkPath);
       }