FIX: git and hg revision checkout under Windows

Windows does not change the working directory for a process via `cd .. && <process>` (see e.g. this question: https://stackoverflow.com/q/55641332/8575607 ). This commit replaces the use of `cd .. &&` with arguments provided by `git` and `hg` respectively.

setuptools/package_index.py

@@ -897,7 +897,7 @@ class PackageIndex(Environment):
 
         if rev is not None:
             self.info("Checking out %s", rev)
-            os.system("(cd %s && git checkout --quiet %s)" % (
+            os.system("git -C %s checkout --quiet %s" % (
                 filename,
                 rev,
             ))
@@ -913,7 +913,7 @@ class PackageIndex(Environment):
 
         if rev is not None:
             self.info("Updating to %s", rev)
-            os.system("(cd %s && hg up -C -r %s -q)" % (
+            os.system("hg --cwd %s up -C -r %s -q" % (
                 filename,
                 rev,
             ))