C++: Add Equals implementation to compare Columns

[asfimport]

The arrow::Column class is missing a method to compare it to other arrow::Column instances. There should be one implemented in the way the Equals implementation is done in the subclasses of arrow::Array and is needed to provide a way to compare arrow::Table instances.

Reporter: Uwe Korn / @xhochy
Assignee: Uwe Korn / @xhochy

Related issues:

• C++: Add Equals implementation to compare Tables (blocks)
• C++: Add Equals implementation to compare ChunkedArrays (is blocked by)

_{Note: This issue was originally created as ARROW-416. Please see the migration documentation for further details.}

[asfimport]

Uwe Korn / @xhochy:
PR: #259

[asfimport]

Wes McKinney / @wesm:
Done in fdbc579