Fixed LaTeX-printing of ConditionSet with FiniteSet

[oscargus]

References to other Issues or PRs

Fixes #15353

Brief description of what is fixed or changed

LaTeX printing of ConditionSet with a FiniteSet used to throw an exception. Now it prints.

ConditionSet((x, a), {sin(a*x), cos(a*x)}, Complexes(Reals x Reals, False))

prints as

No idea if it is correct, but it matches exactly what the issue reporter thought would be a good result and since I only did a minor change, I think it can be correct also for other cases.

Other comments

Release Notes

• printing
  • LaTeX-printing of ConditionSetwith FiniteSet now works.

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• printing
  • LaTeX-printing of ConditionSetwith FiniteSet now works. (#15978 by @oscargus)

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#### References to other Issues or PRs
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Fixes #15353 

#### Brief description of what is fixed or changed
LaTeX printing of ConditionSet with a FiniteSet used to throw an exception. Now it prints.

`ConditionSet((x, a), {sin(a*x), cos(a*x)}, Complexes(Reals x Reals, False))`

prints as

![image](https://user-images.githubusercontent.com/8114497/52733424-fad5fe80-2fc2-11e9-87ce-ea9acf67314b.png)

No idea if it is correct, but it matches exactly what the issue reporter thought would be a good result and since I only did a minor change, I think it can be correct also for other cases.

#### Other comments


#### Release Notes

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<!-- BEGIN RELEASE NOTES -->
* printing
   * LaTeX-printing of `ConditionSet`with `FiniteSet` now works.
<!-- END RELEASE NOTES -->

Update

The release notes on the wiki have been updated.

[oscargus]

I'm taking the liberty of merging some printing related PR without external review. Still better than an error.

[moorepants]

@oscargus FYI, self merging is frowned upon in SymPy. Please get at least 1 person to review.

[asmeurer]

You should test the set directly. The output of solve could change, and anyway it's unnecessary to perform the solve as part of the test.

[oscargus]

@asmeurer Makes sense. I'll make a new PR and let it pass the standard review process.

@moorepants I agree that in general that is clearly for good reasons. However, compared to many other areas, printing, especially getting things that didn't work to work, seems like a relatively non-critical part and somehow it is better for the community to focus on reviewing my other ten or so open PRs that actually affects the behavior. (Although, admittedly, there was something to improve in this particular one.) The main reason to try to merge them rather quickly is to avoid lots of unnecessary test runs caused by merge conflicts in the test files since there is quite a bit of work in that area now. But clearly, I'll try to be more patient.