Trac #14101: Removed CombinatorialClass from skew*.
Trac #14969: Longest Common subword
Trac #14969: implement longest_common_subword (reviewer patch)
Trac #14883: remove a useless multiplication in set_partition_ordered.py
Trac #14981: Implement the descent algebra.
Trac #14334: integration of polynomials and power series wrt any variable
Trac #14806: Immutable graph backend
Trac #14787: Implement N and M statistics on generalized Young walls.
Trac #14787: added mathrsfs to pdf build
Trac #14368: Fix of the problem that DirichletGroup(1).list() returns the zero character in modular/dirichlet.py
Trac #15058: Adding trigonometric and spike functions to documentation
Trac #15058: Review patch for #15058
Trac #15053: Fix embeddings of number fields into fields of non-zero characteristic
Trac #14688: Fix return values in comparison in matrix_integer_2x2
Trac #12183: added absolute and relative norm
Trac #15066: Only look for _graphics_() method in SageObjects.

Pymongo does weird stuff in a getattr hook, and there are probably
other weird python libraries around. This will avoid breaking them in
Sage.
Trac #15042: Cleanup to weyl_characters.py.
Trac #14961: Hack fix to the preparser to not crash with invalid syntax
Trac #14961: Add doctest for preparser SyntaxError in IPython
Trac #15069: Let the MonoDict and TripleDict callbacks return a deleted dictionary value, to keep it alive until the callback is finished