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-rpmbuild.patch

@@ -1,6 +1,6 @@
 diff -up src/module_list.py.orig src/module_list.py
---- src/module_list.py.orig	2019-01-16 09:42:29.021226961 -0700
-+++ src/module_list.py	2019-01-16 09:42:41.397004883 -0700
+--- src/module_list.py.orig	2019-04-08 11:45:44.437520141 -0600
++++ src/module_list.py	2019-04-08 11:45:58.268274982 -0600
 @@ -2,7 +2,7 @@ import os
  from distutils.extension import Extension
  from sage.env import SAGE_LOCAL
@@ -11,21 +11,21 @@ diff -up src/module_list.py.orig src/module_list.py
  #########################################################
  ### pkg-config setup
 diff -up src/sage/misc/cython.py.orig src/sage/misc/cython.py
---- src/sage/misc/cython.py.orig	2018-12-22 16:37:09.000000000 -0700
-+++ src/sage/misc/cython.py	2019-01-04 10:27:47.031123276 -0700
-@@ -600,7 +600,7 @@ def cython(filename, verbose=0, compile_
-     ext = Extension(name,
-                     sources=[pyxfile] + extra_sources,
-                     libraries=libs,
--                    library_dirs=[os.path.join(SAGE_LOCAL, "lib")] + libdirs,
-+                    library_dirs=[os.path.realpath(os.path.join(SAGE_LOCAL, "lib"))] + libdirs,
-                     extra_compile_args=extra_args,
-                     language=language)
+--- src/sage/misc/cython.py.orig	2019-04-08 11:45:58.269274964 -0600
++++ src/sage/misc/cython.py	2019-04-08 11:48:23.582699337 -0600
+@@ -49,7 +49,7 @@ standard_libs = [
+ ] + cblas_libs + [
+     'ntl']
  
+-standard_libdirs = [os.path.join(SAGE_LOCAL, "lib")] + cblas_library_dirs
++standard_libdirs = [os.path.realpath(os.path.join(SAGE_LOCAL, "lib"))] + cblas_library_dirs
+ 
+ 
+ ################################################################
 diff -up src/setup.py.orig src/setup.py
---- src/setup.py.orig	2018-12-22 16:37:10.000000000 -0700
-+++ src/setup.py	2019-01-04 10:27:47.032123257 -0700
-@@ -371,9 +371,8 @@ class sage_build_cython(Command):
+--- src/setup.py.orig	2019-03-23 16:20:43.000000000 -0600
++++ src/setup.py	2019-04-08 11:45:58.283274716 -0600
+@@ -318,9 +318,8 @@ class sage_build_cython(Command):
              # Debugging
              gdb_debug=self.debug,
              output_dir=os.path.join(self.build_lib, "sage"),
@@ -37,7 +37,7 @@ diff -up src/setup.py.orig src/setup.py
              )
  
          # Filter out extensions with skip_build=True
-@@ -882,9 +881,6 @@ class sage_install(install):
+@@ -829,9 +828,6 @@ class sage_install(install):
          install.run(self)
          self.install_kernel_spec()
          log.info('Cleaning up stale installed files....')
@@ -47,7 +47,7 @@ diff -up src/setup.py.orig src/setup.py
  
      def install_kernel_spec(self):
          """
-@@ -901,40 +897,6 @@ class sage_install(install):
+@@ -848,40 +844,6 @@ class sage_install(install):
          # the install_data directory for installing our Jupyter files.
          SageKernelSpec.update(prefix=self.install_data)