tests: fixed "skipped" tests; added more test flags;

test/common.vim:
 * made previous behaviour (of ignoring "skipped" tests) configurable:
    added s:evlib_test_common_ignore_skipped_tests_completely;
  * made default to show which tests (and groups) are skipped;
 * new function EVLibTest_Module_Load();
 * exposed 's:' functions to be global:
  * EVLibTest_Util_ThrowTestException_Custom();
  * EVLibTest_Util_ThrowTestExceptionInternalError();
 * EVLibTest_Do_Check():
  * added flags 'q', 'v';
  * implemented optional "verbose"/"silent" command execution;
 * added comments on new functionality to be added ('TODO:');
 * left a couple of debug-only messages as comments ('FIXME:');
 * EVLibTest_Do_Batch():
  * added new test entry options: 'skiponfail.cont', 'silent',
     'verbose';

test/vimrc_10_selftest-ex-local-nopass.vim:
 * updated checking for number of tests (as tests are now actually
    "skipped", and still counted as non-passes);
 * minor fixes;
added test support for "user scripts" throwing exceptions

TODO:
 * minor updates: marked a few things as "done";

test/libstage.vim: new file: encapsulate library initialisation stages
 testing;
 * utility functions;
 * functions to execute test groups (via
    EVLibTest_GroupSet_LoadLibrary_Method_RuntimePathAdjust());
 * all the testing code for the files:
  * test/vimrc_61_init_libstate_01-ex-local-pass.vim;
  * test/vimrc_62_init_libstate_02-ex-local-pass.vim;
  * test/vimrc_63_init_libstate_03-ex-local-pass.vim;
  * test/vimrc_64_init_libstate_04-ex-local-pass.vim;
  is now implemented in this file;

test/test_trees/init.01/lib/evlib/init/post/85-test1.vim:
test/test_trees/init.01/lib/evlib/init/pre/05-test1.vim:
 * added support for tests with optional per-"user script" throwing
    policies;
  * use:
   * EVLibTest_LibStages_UserScriptWouldThrow();
   * EVLibTest_LibStages_UserScriptConditionallyThrow();
   * EVLibTest_LibStages_CheckUpdateCounter() (this one was used in the
      previous version);

test/vimrc_61_init_libstate_01-ex-local-pass.vim:
test/vimrc_62_init_libstate_02-ex-local-pass.vim:
test/vimrc_63_init_libstate_03-ex-local-pass.vim:
test/vimrc_64_init_libstate_04-ex-local-pass.vim:
 * created/modified scripts to use the new functions:
  * EVLibTest_Module_Load();
  * EVLibTest_LibStages_FullSuite_UserScriptThrow();