* 994e38e3 "loplugin: use TypeCheck instead of
  getQualifiedNameAsString" had effectively disabled this plugin (Asserter is a
  struct, not a namespace).  Fixed that.

* Also improved the checks, for one removing the---expensive---use of
  Plugin::parentStmt, for another making the plugin look into (...), !..., and
  ...&&... expressions.

* However, as the plugin had effectively already been disabled (see above) when
  it was switched on generally with 839e53b9
  "compilerplugins: enable loplugin:cppunitassertequals by default", it now hit
  way more places than I had initially anticipated.  To keep the amount of work
  manageable, midway-through I disabled looking into ...&&... expressions for
  now.  That will be enabled (and resulting warnings fixed) in follow-up
  commits.

* Checks like

    CPPUNIT_ASSERT(a == b)

  that actually want to check a specific overloaded operator == implementation,
  rather than using such an operator == to actually check that a and b are
  equal, can be rewritten as

    CPPUNIT_ASSERT(operator ==(a, b))

  to avoid false warnings from this plugin.

Change-Id: If3501020e2d150ad0f2454a65a39081e31470c0f