[C++] Implement hash kernel specialization for BooleanType

[asfimport]

Follow up to ARROW-1559

Reporter: Wes McKinney / @wesm
Assignee: Wes McKinney / @wesm

PRs and other links:

• GitHub Pull Request #1350

_{Note: This issue was originally created as ARROW-1828. Please see the migration documentation for further details.}

[asfimport]

Wes McKinney / @wesm:
Issue resolved by pull request 1350
#1350