Update to sagemath 8.7.

- Drop upstreamed -giac patch.
- Add -sagetex patch to fix a python indentation error.
- Add -rubiks patch to fix compilation of the rubiks library.
- Add -random patch to fix a non-random random bit generator.
- Drop pip3 workaround; the binary is now named just pip again.

sagemath-qepcad.patch

@@ -1,6 +1,6 @@
 diff -up src/sage/interfaces/qepcad.py.orig src/sage/interfaces/qepcad.py
---- src/sage/interfaces/qepcad.py.orig	2018-12-22 16:37:08.000000000 -0700
-+++ src/sage/interfaces/qepcad.py	2019-01-16 09:46:44.714638633 -0700
+--- src/sage/interfaces/qepcad.py.orig	2019-03-23 16:20:41.000000000 -0600
++++ src/sage/interfaces/qepcad.py	2019-04-08 13:32:00.509789984 -0600
 @@ -530,7 +530,7 @@ TESTS:
  
  Check the qepcad configuration file::
@@ -10,16 +10,16 @@ diff -up src/sage/interfaces/qepcad.py.orig src/sage/interfaces/qepcad.py
      ....:     f.readlines()[-1]
      'SINGULAR .../bin\n'
  
-@@ -608,7 +608,6 @@ from __future__ import print_function
- from __future__ import absolute_import
+@@ -607,7 +607,6 @@ AUTHORS:
+ from __future__ import print_function, absolute_import
  from six import string_types
  
 -from sage.env import SAGE_LOCAL
  import pexpect
  import re
  import sys
-@@ -621,6 +620,8 @@ from sage.docs.instancedoc import instan
- from .expect import Expect, ExpectFunction, AsciiArtString
+@@ -621,6 +620,8 @@ from .expect import Expect, ExpectFuncti
+ from sage.interfaces.interface import AsciiArtString
  
  
 +QEPCAD_LOCAL = "/usr/share/qepcad"