catch by const reference

[bgoodri]

Summary

This pull request changes

catch (boost::bad_lexical_cast)

to

catch (const boost::bad_lexical_cast&)

and fixes #1608

Tests

None

Side Effects

Eliminates a warning

Checklist

• Math issue catch by constant reference #1608

• Copyright holder: Trustees of 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)
  • 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

[rok-cesnovar]

Thanks!

[stan-buildbot]

---

Name	Old Result	New Result	Ratio	Performance change( 1 - new / old )
gp_pois_regr/gp_pois_regr.stan	4.87	4.84	1.01	0.78% faster
low_dim_corr_gauss/low_dim_corr_gauss.stan	0.02	0.02	0.99	-0.89% slower
eight_schools/eight_schools.stan	0.09	0.09	0.98	-2.13% slower
gp_regr/gp_regr.stan	0.22	0.23	0.98	-1.58% slower
irt_2pl/irt_2pl.stan	6.1	6.08	1.0	0.26% faster
performance.compilation	87.8	86.84	1.01	1.09% faster
low_dim_gauss_mix_collapse/low_dim_gauss_mix_collapse.stan	7.33	7.29	1.0	0.49% faster
pkpd/one_comp_mm_elim_abs.stan	20.86	20.31	1.03	2.64% faster
sir/sir.stan	98.46	104.7	0.94	-6.33% slower
gp_regr/gen_gp_data.stan	0.05	0.05	1.0	0.38% faster
low_dim_gauss_mix/low_dim_gauss_mix.stan	3.12	2.97	1.05	4.74% faster
pkpd/sim_one_comp_mm_elim_abs.stan	0.32	0.32	0.98	-2.07% slower
arK/arK.stan	2.42	1.8	1.34	25.47% faster
arma/arma.stan	0.8	0.73	1.1	9.09% faster
garch/garch.stan	0.52	0.52	1.0	0.28% faster
Mean result: 1.02843186906

---

Jenkins Console Log
[Blue Ocean](https://jenkins.mc-stan.org/blue/organizations/jenkins/Math Pipeline/detail/PR-1609/897/pipeline)
Commit hash: 98a8cad

---

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