Changed since 55bf0ef1aa7c936b564b883196de1ace4be4cc7e.

As `make test-tool` does not use gems, and no Rubygems stuffs is
needed, so moved such things to test/runner.rb.  Also no longer
nees `--test-target-dir` option.

tool/test/runner.rb had been copied from test/runner.rb.
test/runner.rb was for `make test-all`, and tool/test/runner.rb was for
`make test-testframework` and `make test-tool`.
But I want to avoid the code clones.

This change makes tool/test/runner.rb support --test-target-dir option
which allows tool/test/runner.rb to run `make test-all`.
Now we can remove test/runner.rb.

  ref. c3c0e3f5c9444c197779cb242de46dfffda79dec

* test/runner.rb (COVERAGE): should use require_relative instead of require,
  because the working directory may not be srcdir.


git-svn-id: svn+ssh://ci.ruby-lang.org/ruby/trunk@59773 b2dd03c8-39d4-4d8f-98ff-823fe69b080e

Now `make test-all COVERAGE=true` measures the test coverage by using
`coverage.so` directly, and visualize the result by simplecov-html.

There has been some problems in coverage measurement with SimpleCov.
(They are not SimpleCov's fault, though.)

(1) It is difficult to extract the measured data as a machine-readable
format, such as Marshal.  I want to visualize the coverage data with
other coverage tools, such as LCOV and Cobertura.
(I know we can use SimpleCov's formatter mechanism, but I don't want
to depend upon SimpleCov so much.)

(2) SimpleCov seems to miss some coverage data.  For example,
`lib/cgi.rb` and `lib/ostruct.rb` are dropped.  I don't know why.

(3) I have a plan to enhance `coverage.so` with branch coverage.
It would be difficult to continue to only use SimpleCov as is.
This is the most important reason.

git-svn-id: svn+ssh://ci.ruby-lang.org/ruby/trunk@59770 b2dd03c8-39d4-4d8f-98ff-823fe69b080e