Make more function values be exact, when possible#16

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bobcassels wants to merge 4 commits intojtobey:masterfrom

angeni8:more-exact-function-values

Commits on Mar 16, 2017

Make sqrt of exact integer, rational, complex be exact when appropriate.
bobcassels
committed

Commits on Mar 19, 2017

Expt 0 0 is an error only if both are exact.
bobcassels
committed

Commits on Mar 20, 2017

Fix some issues with lcm, expt, and log.
bobcassels
committed

Commits on May 6, 2017

Fix complex sqrt, reciprocal, and divide, when complex infinities are involved.
bobcassels
committed