Implement RealSet - finite unions of open/closed/semi-closed subsets of the real line.
Further improvements to RealSet
Trac #13125: reviewer's patch: fix typos, add module to set refman
Merge branch 'develop' into ticket/13125
Use a UniqueFactory to cache instances of DirichletGroup

Before some generic caching was used. This should be more robust, easier to maintain, and faster.
Doctest to illustrate that caching of DirichletGroups works
Doctest to illustrate that base_ring must be a part of the cache key created by the DirichletGroup factory
cleaned up docstring of DirichletGroup
Merge branch 'u/saraedum/ticket/15898' of git://trac.sagemath.org/sage into ticket/15898-DirichletGroup_unique

Conflicts:
	src/sage/modular/dirichlet.py
Trac #15898: UniqueFactory for DirichletGroup

Dirichlet groups use a generic dictionary to cache objects (instead of
UniqueRepresentation or UniqueFactory). This ticket replaces this
generic cache with a UniqueFactory implementation.

URL: http://trac.sagemath.org/15898
Reported by: saraedum
Ticket author(s): Julian Rueth
Reviewer(s): Peter Bruin
add tests for comparison of infinity with other ring elements
fix element constructor of the infinity ring
handle conversion of RIF into InfinityRing
Trac #13125: Reals sets consisting of intervals and isolated points

Finite unions of open/closed/semi-closed subsets of the real line, for
example
{{{
    sage: RealSet(0,2) + RealSet.unbounded_above_closed(10)
    (0, 2) + [10, +Infinity)
}}}

This ticket also encountered a number of bugs in the comparison of
infinity with various field elements like
{{{
sage: RLF(0) < oo
False
}}}
These are now also fixed and extensive doctests were added.

URL: http://trac.sagemath.org/13125
Reported by: ares
Ticket author(s): Volker Braun , Jordi Saludes , Ares Ribó
Reviewer(s): Ralf Stephan