python-requests2: use system-wide CA bundle rather than our own

This allows the library to interact gracefully with additional certificates
users might have configured in /etc/ssl/certs/ca-certificates.crt via NixOS.

pkgs/development/python-modules/requests/0001-requests-certs.py-use-system-wide-cert-bundle-from-N.patch

@@ -0,0 +1,43 @@
+From f04105df552309880ede3176c48930762843ea8d Mon Sep 17 00:00:00 2001
+From: Peter Simons <simons@cryp.to>
+Date: Thu, 9 Feb 2017 15:06:36 +0100
+Subject: [PATCH] requests/certs.py: use system-wide cert bundle from NixOS
+ rather than our own
+
+---
+ requests/certs.py | 17 ++++-------------
+ 1 file changed, 4 insertions(+), 13 deletions(-)
+
+diff --git a/requests/certs.py b/requests/certs.py
+index f922b99d..0209ecc2 100644
+--- a/requests/certs.py
++++ b/requests/certs.py
+@@ -5,21 +5,12 @@
+ requests.certs
+ ~~~~~~~~~~~~~~
+ 
+-This module returns the preferred default CA certificate bundle.
+-
+-If you are packaging Requests, e.g., for a Linux distribution or a managed
+-environment, you can change the definition of where() to return a separately
+-packaged CA bundle.
++This module returns the preferred default CA certificate bundle (for NixOS).
+ """
+-import os.path
+ 
+-try:
+-    from certifi import where
+-except ImportError:
+-    def where():
+-        """Return the preferred certificate bundle."""
+-        # vendored bundle inside Requests
+-        return os.path.join(os.path.dirname(__file__), 'cacert.pem')
++def where():
++    """Return the preferred certificate bundle."""
++    return "/etc/ssl/certs/ca-certificates.crt"
+ 
+ if __name__ == '__main__':
+     print(where())
+-- 
+2.11.1
+

pkgs/top-level/python-packages.nix

@@ -22082,7 +22082,6 @@ in {
     };
   };
 
-
   requests = buildPythonPackage rec {
     name = "requests-1.2.3";
     disabled = !pythonOlder "3.4";
@@ -22098,7 +22097,6 @@ in {
     };
   };
 
-
   requests2 = buildPythonPackage rec {
     name = "requests-${version}";
     version = "2.13.0";
@@ -22108,6 +22106,8 @@ in {
       sha256 = "5722cd09762faa01276230270ff16af7acf7c5c45d623868d9ba116f15791ce8";
     };
 
+    patches = [../development/python-modules/requests/0001-requests-certs.py-use-system-wide-cert-bundle-from-N.patch];
+
     nativeBuildInputs = [ self.pytest ];
     # sadly, tests require networking
     doCheck = false;