expectThat doesn't report the line number of failed expectations

[Robert Collins]

e.g.:

FAIL: pbr.tests.test_version.TestSemanticVersion.test_ordering
tags: worker-0
----------------------------------------------------------------------
Empty attachments:
  pythonlogging:''
  pythonlogging:'pbr'
  stderr
  stdout

Failed expectation: {{{
MismatchError: is not >:
reference = pbr.version.SemanticVersion(1.2.3.0a4.dev12)
actual = pbr.version.SemanticVersion(1.2.3.dev6)
}}}

Failed expectation-1: {{{
MismatchError: is not <:
reference = pbr.version.SemanticVersion(1.2.3.dev6)
actual = pbr.version.SemanticVersion(1.2.3.0a4.dev12)
}}}

Traceback (most recent call last):
AssertionError: Forced Test Failure