Install dependencies before the depending.

This appears to be a fix for a regression vs master, as it passes tests.  I
found the issue when working on setup-requires, as in that case a failure
doesn't just break after pip completes, but actually causes the pip invocation
to fail. See issue 2260 in the discussion where its stated that installing
deps first is desired.

pip/req/req_set.py

@@ -506,6 +506,13 @@ def _prepare_file(self, finder, req_to_install):
  dist = abstract_dist.dist(finder)
  more_reqs = []
 
+ # We add req_to_install before its dependencies, so that when
+ # to_install is calculated, which reverses the order,
+ # req_to_install is installed after its dependencies.
+ if not self.has_requirement(req_to_install.name):
+ # 'unnamed' requirements will get added here
+ self.add_requirement(req_to_install)
+
  if not self.ignore_dependencies:
  if (req_to_install.extras):
  logger.debug(
@@ -536,10 +543,6 @@ def _prepare_file(self, finder, req_to_install):
  more_reqs.append(subreq)
  self.add_requirement(subreq)
 
- if not self.has_requirement(req_to_install.name):
- # 'unnamed' requirements will get added here
- self.add_requirement(req_to_install)
-
  # cleanup tmp src
  self.reqs_to_cleanup.append(req_to_install)