Make wishart and inv_wishart functions check symmetry/positive definiteness on input

[bbbales2]

Summary

This is a fix for #2279 . It makes it so that wishart_lpdf, wishart_log, wishart_rng, inv_wishart_lpdf, inv_wishart_log, and inv_wishart_rng check that their matrix arguments are symmetric and positive definite.

Tests

I added new positive definite tests to the prim tests. I also updated all the old tests so that only symmetric, positive definite inputs work

Release notes

• Wishart and inverse wishart functions now check that symmetric positive definite inputs are actually symmetric positive definite.

Checklist

• Math issue The wishart distributions are documented to only accept symmetric matrices but actually do accept asymmetric matrices #2279

• Copyright holder: Columbia University

  The copyright holder is typically you or your assignee, such as a university or company. By submitting this pull request, the copyright holder is agreeing to the license the submitted work under the following licenses:
  - Code: BSD 3-clause (https://opensource.org/licenses/BSD-3-Clause)
  - Documentation: CC-BY 4.0 (https://creativecommons.org/licenses/by/4.0/)

• the basic tests are passing

  • unit tests pass (to run, use: ./runTests.py test/unit)
  • header checks pass, (make test-headers)
  • dependencies checks pass, (make test-math-dependencies)
  • docs build, (make doxygen)
  • code passes the built in C++ standards checks (make cpplint)

• the code is written in idiomatic C++ and changes are documented in the doxygen

• the new changes are tested

[stan-buildbot]

---

Name	Old Result	New Result	Ratio	Performance change( 1 - new / old )
gp_pois_regr/gp_pois_regr.stan	3.32	3.34	0.99	-0.66% slower
low_dim_corr_gauss/low_dim_corr_gauss.stan	0.02	0.02	1.0	-0.22% slower
eight_schools/eight_schools.stan	0.11	0.11	0.98	-1.57% slower
gp_regr/gp_regr.stan	0.16	0.16	1.01	0.58% faster
irt_2pl/irt_2pl.stan	5.17	5.14	1.01	0.64% faster
performance.compilation	91.07	88.57	1.03	2.74% faster
low_dim_gauss_mix_collapse/low_dim_gauss_mix_collapse.stan	8.66	8.66	1.0	0.06% faster
pkpd/one_comp_mm_elim_abs.stan	28.37	29.9	0.95	-5.42% slower
sir/sir.stan	136.68	131.79	1.04	3.58% faster
gp_regr/gen_gp_data.stan	0.04	0.04	1.0	-0.45% slower
low_dim_gauss_mix/low_dim_gauss_mix.stan	3.04	3.05	1.0	-0.26% slower
pkpd/sim_one_comp_mm_elim_abs.stan	0.38	0.38	1.0	-0.29% slower
arK/arK.stan	2.53	2.54	1.0	-0.44% slower
arma/arma.stan	0.61	0.61	0.99	-1.0% slower
garch/garch.stan	0.67	0.68	1.0	-0.3% slower
Mean result: 0.998344698235

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Jenkins Console Log
Blue Ocean
Commit hash: 5151f64

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Machine information

ProductName: Mac OS X ProductVersion: 10.11.6 BuildVersion: 15G22010

CPU:
Intel(R) Xeon(R) CPU E5-1680 v2 @ 3.00GHz

G++:
Configured with: --prefix=/Applications/Xcode.app/Contents/Developer/usr --with-gxx-include-dir=/usr/include/c++/4.2.1
Apple LLVM version 7.0.2 (clang-700.1.81)
Target: x86_64-apple-darwin15.6.0
Thread model: posix

Clang:
Apple LLVM version 7.0.2 (clang-700.1.81)
Target: x86_64-apple-darwin15.6.0
Thread model: posix

[bbbales2]

Ready for review! #2266 needs this in

[syclik]

Lgtm!