Add rtx.ErrorLoggingCloser to wrap Close() and log errors.

[robertodauria]

Discussed with @stephen-soltesz during a call. This might be useful to simplify some code where we want to not ignore the error returned by a deferred call.

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This change is 

[coveralls]

Pull Request Test Coverage Report for Build 329

• 9 of 9 (100.0%) changed or added relevant lines in 1 file are covered.
• No unchanged relevant lines lost coverage.
• Overall coverage increased (+0.5%) to 72.085%

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Totals
Change from base Build 313:	0.5%
Covered Lines:	408
Relevant Lines:	566

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💛 - Coveralls

[pboothe]

Could also do:

/*interface Closer {
  func Close() error
}
*/

struct errorLoggingCloser {
  c io.Closer
}

func (elc *errorLoggingCloser) Close() error {
  err := elc.c.Close()
  if err != nil {
    log.Println(err)
  }
  return err
}

func ErrorLoggingCloser(c Closer) Closer {
  return errorLoggingCloser{c}
}

then this could be used like:

defer ErrorLoggingCloser(f).Close()

[pboothe]

A function which will error out if called too soon.

func TestDeferHappensInTheRightOrder(t *testing.T) {
  okay := false
  func f() {
    if !okay {
      t.Error("Deferred function called too soon")
    }
  }
  defer Should(f(), "defer doesn't work the way you might think it should")
  okay = true
  // This test will fail.
}

[pboothe]

Don't forget to update the package name in the go files!