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-latte.patch

@@ -0,0 +1,21 @@
+diff -up src/sage/interfaces/latte.py.orig src/sage/interfaces/latte.py
+--- src/sage/interfaces/latte.py.orig	2019-01-16 09:44:45.946769879 -0700
++++ src/sage/interfaces/latte.py	2019-01-16 09:47:33.355765786 -0700
+@@ -112,7 +112,7 @@ def count(arg, ehrhart_polynomial=False,
+     # Check that LattE is present
+     Latte().require()
+ 
+-    args = ['count']
++    args = ['latte-count']
+     if ehrhart_polynomial and multivariate_generating_function:
+         raise ValueError
+     if ehrhart_polynomial:
+@@ -305,7 +305,7 @@ def integrate(arg, polynomial=None, algo
+     # Check that LattE is present
+     Latte().require()
+ 
+-    args = ['integrate']
++    args = ['latte-integrate']
+ 
+     got_polynomial = True if polynomial is not None else False
+