Update to sagemath 8.5.

Also:
- Bundle ipython again; Fedora version is too far ahead.  Also have to bundle
  prompt_toolkit since Fedora version is too far ahead of bundled ipython.
- Drop LANGUAGES variable setting, now ignored by the sagemath build system.
- Drop unused SAGE_CBLAS variable from /usr/bin/sage.
- Do not force the C locale when launching sagemath.
- Allow the user to override SAGE_DEBUG in /usr/bin/sage.
- Add -ecm, -giac, and -latte patches to fix interactions with external tools.
- Add -sigfpe patch from upstream.

sagemath-ecm.patch

@@ -0,0 +1,12 @@
+diff -up src/sage/interfaces/ecm.py.orig src/sage/interfaces/ecm.py
+--- src/sage/interfaces/ecm.py.orig	2018-12-22 16:37:08.000000000 -0700
++++ src/sage/interfaces/ecm.py	2019-01-15 10:26:31.060040736 -0700
+@@ -256,7 +256,7 @@ class ECM(SageObject):
+         """
+         print("Enter numbers to run ECM on them.")
+         print("Press control-C to exit.")
+-        os.system(self._cmd)
++        os.system(' '.join(self._cmd))
+ 
+     # Recommended settings from
+     # http://www.mersennewiki.org/index.php/Elliptic_Curve_Method