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
add tests for comparison of infinity with other ring elements
fix element constructor of the infinity ring
handle conversion of RIF into InfinityRing
also handle conversion of symbolic infinity
Merge branch 'develop' into t/13125/ticket/13125

Conflicts:
	src/sage/sets/all.py
strip out grant acknowledgement
Merge branch 'develop' into t/13125/real_sets

Conflicts:
	src/sage/sets/all.py
also add conversion (not: coercion) for CC -> infinity ring
fix addition/subtraction of unsigned infinity
forbid conversion from unsigned infinity to RR, RDF
also accept %display typeset in ipython
document the RIF comparison with infinity
fix merge conflict with #14329
fix merge conflict with #14329
fix docbuild due to backslash in output
Trac #16368: Missing pkgconf dependencies

We should build the pkgconf package before anything that uses pkg-
config.

URL: http://trac.sagemath.org/16368
Reported by: stephen
Ticket author(s): Volker Braun
Reviewer(s): Martin Albrecht