new test functionality (group options); improved selftest;

 * test/common.vim:
  * EVLibTest_Gen_InfoVarValue(): added optional message prefix;
  * EVLibTest_Group_End():
   * extended/fixed: if a particular test was skipped, this function was
      propagating the test's "skipping policy", as if the test had
      executed and failed.  It is now correctly refraining from updating
      any status variables when a test has been skipped;
  * EVLibTest_Do_Check(): improved code resistance: when an evaluated
     expression returns a value whose type isn't a 'number', this
     function now maps the value to "false";
  * EVLibTest_Internal_TestFlagsUpdate():
   * implements the generic mechanism by which a flags string value gets
      manipulated by "user options" specified in a list (usually from an
      'options' group/test dictionary entry), including validating those
      options against a caller-supplied list;
  * EVLibTest_Do_Batch():
   * implement the concept of "global", "group", and "test" options
      (previously, only "test" options were available), with each set of
      options overriding the previous one ("group" overrides the
      "global", "test" overrides the "group", etc.), if specified;
   * minor updates;
  * left some "debug" code (search for '[debug]' and 'FIXME:') -- to be
     removed later;;

 * test/vimrc_10_selftest-ex-local-nopass.vim:
  * reformatted previous suite to be an instance of a (new) suite set
     now;
  * added new suite '#10.2', with an extensive "results validation"
     matching suite;
   * tests for new "group options" functionality (including "test
      option overrides");
  * removed dead code;
test/bin/run-tests.sh: minor improvements
tests: improvements (scripts, results checking);

 * test/bin/run-tests.sh:
  * filtering: added support for '[custom.pass]' lines ('^RESULTS '):
     groups and suites can be deemed as "pass" if there is such an entry
     (regardless of the number of failed tests/groups that would
     indicate otherwise);

 * test/common.vim:
  * EVLibTest_Finalise(): added support for user-specified results
     checking (that would create the aforementioned '[custom.pass]'
     entries in the suite);
  * EVLibTest_Gen_CheckTestStats():
   * allows the caller to specify its own test results (defaults to
      calling EVLibTest_Gen_GetTestStats());
   * s:EVLibTest_Gen_CheckTestStats_DoDict(): low-level function
      implementing the actual checking (calls itself recursively);
  * EVLibTest_Gen_OutputTestStats():
   * added support for src_results_user;
   * extended output format ('[custom.pass]'/'[custom.FAIL]');
  * EVLibTest_Group_End(): added support for user-specified results
     checking;

 * test/vimrc_10_selftest-ex-local-pass.vim:
  * renamed (old name: 'test/vimrc_10_selftest-ex-local-nopass.vim');
  * added support for user-specified results checking
     (EVLibTest_Finalise());