support concurrent btest execution

* `-j` option for concurrent test with threads
  * `-jN` uses N threads
  * `-j` uses nproc/2 threads
* Introduce `BT` struct to manage configurations
* Introduce `Assertion` to manage all assertions
* Remove all toplevel instance variables
* Show elapsed seconds at last

```
$ time make btest
...
real    0m37.319s
user    0m26.221s
sys     0m16.534s

$ time make btest TESTOPTS=-j
...
real    0m11.812s
user    0m36.667s
sys     0m21.872s
```

1 files changed, 15 insertions, 15 deletions

diff --git a/bootstraptest/test_autoload.rb b/bootstraptest/test_autoload.rb
index a9f8e6dacd..9e0850bc52 100644
--- a/bootstraptest/test_autoload.rb
+++ b/bootstraptest/test_autoload.rb
@@ -1,7 +1,7 @@
 assert_equal 'ok', %q{
-  File.unlink('zzz.rb') if File.file?('zzz.rb')
+  File.unlink('zzz1.rb') if File.file?('zzz1.rb')
   instance_eval do
-    autoload :ZZZ, './zzz.rb'
+    autoload :ZZZ, './zzz1.rb'
     begin
       ZZZ
     rescue LoadError
@@ -11,9 +11,9 @@ assert_equal 'ok', %q{
 }, '[ruby-dev:43816]'
 
 assert_equal 'ok', %q{
-  open('zzz.rb', 'w') {|f| f.puts '' }
+  open('zzz2.rb', 'w') {|f| f.puts '' }
   instance_eval do
-    autoload :ZZZ, './zzz.rb'
+    autoload :ZZZ, './zzz2.rb'
     begin
       ZZZ
     rescue NameError
@@ -23,29 +23,29 @@ assert_equal 'ok', %q{
 }, '[ruby-dev:43816]'
 
 assert_equal 'ok', %q{
-  open('zzz.rb', 'w') {|f| f.puts 'class ZZZ; def self.ok;:ok;end;end'}
+  open('zzz3.rb', 'w') {|f| f.puts 'class ZZZ; def self.ok;:ok;end;end'}
   instance_eval do
-    autoload :ZZZ, './zzz.rb'
+    autoload :ZZZ, './zzz3.rb'
     ZZZ.ok
   end
 }, '[ruby-dev:43816]'
 
 assert_equal 'ok', %q{
-  open("zzz.rb", "w") {|f| f.puts "class ZZZ; def self.ok;:ok;end;end"}
-  autoload :ZZZ, "./zzz.rb"
+  open("zzz4.rb", "w") {|f| f.puts "class ZZZ; def self.ok;:ok;end;end"}
+  autoload :ZZZ, "./zzz4.rb"
   ZZZ.ok
 }
 
 assert_equal 'ok', %q{
-  open("zzz.rb", "w") {|f| f.puts "class ZZZ; def self.ok;:ok;end;end"}
-  autoload :ZZZ, "./zzz.rb"
-  require "./zzz.rb"
+  open("zzz5.rb", "w") {|f| f.puts "class ZZZ; def self.ok;:ok;end;end"}
+  autoload :ZZZ, "./zzz5.rb"
+  require "./zzz5.rb"
   ZZZ.ok
 }
 
 assert_equal 'okok', %q{
-  open("zzz.rb", "w") {|f| f.puts "class ZZZ; def self.ok;:ok;end;end"}
-  autoload :ZZZ, "./zzz.rb"
+  open("zzz6.rb", "w") {|f| f.puts "class ZZZ; def self.ok;:ok;end;end"}
+  autoload :ZZZ, "./zzz6.rb"
   t1 = Thread.new {ZZZ.ok}
   t2 = Thread.new {ZZZ.ok}
   [t1.value, t2.value].join
@@ -60,9 +60,9 @@ assert_finish 5, %q{
 }, '[ruby-core:21696]'
 
 assert_equal 'A::C', %q{
-  open("zzz.rb", "w") {}
+  open("zzz7.rb", "w") {}
   class A
-    autoload :C, "./zzz"
+    autoload :C, "./zzz7"
     class C
     end
     C