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-giac.patch

@@ -0,0 +1,15 @@
+diff -up src/sage/interfaces/giac.py.orig src/sage/interfaces/giac.py
+--- src/sage/interfaces/giac.py.orig	2018-12-22 16:37:08.000000000 -0700
++++ src/sage/interfaces/giac.py	2019-01-15 15:10:47.399759655 -0700
+@@ -617,10 +617,7 @@ If you got giac from the spkg then ``$PR
+             '4\n3'
+             sage: s='g(x):={\nx+1;\nx+2;\n}'
+             sage: giac(s)
+-            (x)->{
+-            x+1;
+-            x+2;
+-            }
++            (x)->[x+1,x+2]
+             sage: giac.g(5)
+             7
+         """