Properly exclude test cases.

	Lets consider the following scenario:

	~~~
	irb(#<Test::Unit::AutoRunner::Runner:0x0000560f68afc3c8>):001:0> p suite
	OpenSSL::TestEC
	=> OpenSSL::TestEC

	irb(#<Test::Unit::AutoRunner::Runner:0x0000560f68afc3c8>):002:0> p all_test_methods
	["test_ECPrivateKey", "test_ECPrivateKey_encrypted", "test_PUBKEY", "test_check_key", "test_derive_key", "test_dh_compute_key", "test_dsa_sign_asn1_FIPS186_3", "test_ec_group", "test_ec_key", "test_ec_point", "test_ec_point_add", "test_ec_point_mul", "test_generate", "test_marshal", "test_sign_verify", "test_sign_verify_raw"]
	=>
	["test_ECPrivateKey",
	 "test_ECPrivateKey_encrypted",
	 "test_PUBKEY",
	 "test_check_key",
	 "test_derive_key",
	 "test_dh_compute_key",
	 "test_dsa_sign_asn1_FIPS186_3",
	 "test_ec_group",
	 "test_ec_key",
	 "test_ec_point",
	 "test_ec_point_add",
	 "test_ec_point_mul",
	 "test_generate",
	 "test_marshal",
	 "test_sign_verify",
	 "test_sign_verify_raw"]

	irb(#<Test::Unit::AutoRunner::Runner:0x0000560f68afc3c8>):003:0> p filter
	/\A(?=.*)(?!.*(?-mix:(?-mix:memory_leak)|(?-mix:OpenSSL::TestEC.test_check_key)))/
	=> /\A(?=.*)(?!.*(?-mix:(?-mix:memory_leak)|(?-mix:OpenSSL::TestEC.test_check_key)))/

	irb(#<Test::Unit::AutoRunner::Runner:0x0000560f68afc3c8>):004:0> method = "test_check_key"
	=> "test_check_key"
	~~~

	The intention here is to exclude the `test_check_key` test case.
	Unfortunately this does not work as expected, because the negative filter
	is never checked:

	~~~
	irb(#<Test::Unit::AutoRunner::Runner:0x0000560f68afc3c8>):005:0> filter === method
	=> true

	irb(#<Test::Unit::AutoRunner::Runner:0x0000560f68afc3c8>):006:0> filter === "#{suite}##{method}"
	=> false

	irb(#<Test::Unit::AutoRunner::Runner:0x0000560f68afc3c8>):007:0> filter === method || filter === "#{suite}##{method}"
	=> true
	~~~

	Therefore always filter against the fully qualified method name
	`#{suite}##{method}`, which should provide the expected result.

	However, if plain string filter is used, keep checking also only the
	method name.

	This resolves [Bug #16936].
	---
	 tool/lib/test/unit.rb | 12 +++++++++---
	 1 file changed, 9 insertions(+), 3 deletions(-)

	Filter method names only if filtering method name only

	If sole `filter` option doesn't seem including test case name,
	match with method name only.
	And if the filter is a Regexp or String, it never matches method
	name symbols.
	---
	 tool/lib/test/unit.rb | 15 ++++++---------
	 1 file changed, 6 insertions(+), 9 deletions(-)