Improve GLPK error handling

[jdemeyer]

This ticket adds a proper error handler for GLPK (similar to what we already have for PARI, NTL, ...). It suffices to add sig_on()/sig_off() around a GLPK call to get an error message.

Some more cleanup is also done:

1. change the implementation of MIPSolverException to just inherit from RuntimeError without any custom implementation.
2. use MemoryAllocator in a few places to make some allocations safer.

This branch requires a patch to GLPK, a modified version of it was accepted upstream: http://lists.gnu.org/archive/html/help-glpk/2015-11/msg00008.html

Upstream: Fixed upstream, in a later stable release.

CC: @nathanncohen

Component: cython

Author: Jeroen Demeyer

Branch/Commit: 76a11fd

Reviewer: Vincent Delecroix

Issue created by migration from https://trac.sagemath.org/ticket/19525

[jdemeyer]

Dependencies: #19527

[jdemeyer]

Branch: u/jdemeyer/improve_glpk_error_handling

[sagetrac-git]

Branch pushed to git repo; I updated commit sha1. This was a forced push. New commits:

f808061

Implement GLPK error handling

[sagetrac-git]

Commit: f808061

[jdemeyer]

Upstream: Reported upstream. No feedback yet.

[jdemeyer]

Description changed:

--- 
+++ 
@@ -1 +1,7 @@
+This ticket adds a proper error handler for GLPK (similar to what we already have for PARI, NTL, ...). It suffices to add `sig_on()`/`sig_off()` around a GLPK call to get an error message.
 
+Some more cleanup is also done:
+1. change the implementation of `MIPSolverException` to just inherit from `RuntimeError` without any custom implementation.
+2. use `MemoryAllocator` in a few places to make some allocations safer.
+
+This branch requires a patch to GLPK which has been submitted upstream.

[jdemeyer]

Description changed:

--- 
+++ 
@@ -4,4 +4,4 @@
 1. change the implementation of `MIPSolverException` to just inherit from `RuntimeError` without any custom implementation.
 2. use `MemoryAllocator` in a few places to make some allocations safer.
 
-This branch requires a patch to GLPK which has been submitted upstream.
+This branch requires a patch to GLPK which has been submitted upstream: [http://lists.gnu.org/archive/html/help-glpk/2015-11/msg00008.html](http://lists.gnu.org/archive/html/help-glpk/2015-11/msg00008.html)

[sagetrac-git]

Branch pushed to git repo; I updated commit sha1. New commits:

f312818

Improve printing of solver exceptions

[sagetrac-git]

Changed commit from f808061 to f312818

[jdemeyer]

Changed upstream from Reported upstream. No feedback yet. to Reported upstream. Developers acknowledge bug.