Move specs to "OS thread support" into async file

These specs don't run reliable with sync methods.
They sometimes block indefinitely.

spec/pg/connection_async_spec.rb

@@ -108,4 +108,32 @@ def interrupt_thread(exc=nil)
 		expect( signal_received ).to be_truthy
 	end
 
+	context "OS thread support" do
+		it "Connection#exec shouldn't block a second thread" do
+			t = Thread.new do
+				@conn.exec( "select pg_sleep(1)" )
+			end
+
+			sleep 0.1
+			expect( t ).to be_alive()
+			t.kill
+			@conn.cancel
+		end
+
+		it "Connection.new shouldn't block a second thread" do
+			serv = nil
+			t = Thread.new do
+				serv = TCPServer.new( '127.0.0.1', 54320 )
+				expect {
+					described_class.connect( '127.0.0.1', 54320, "", "", "me", "xxxx", "somedb" )
+				}.to raise_error(PG::ConnectionBad, /server closed the connection unexpectedly/)
+			end
+
+			sleep 0.5
+			expect( t ).to be_alive()
+			serv.close
+			t.join
+		end
+	end
+
 end

spec/pg/connection_spec.rb

@@ -2167,34 +2167,6 @@
 		end
 	end
 
-	context "OS thread support" do
-		it "Connection#exec shouldn't block a second thread" do
-			t = Thread.new do
-				@conn.exec( "select pg_sleep(1)" )
-			end
-
-			sleep 0.1
-			expect( t ).to be_alive()
-			t.kill
-			@conn.cancel
-		end
-
-		it "Connection.new shouldn't block a second thread" do
-			serv = nil
-			t = Thread.new do
-				serv = TCPServer.new( '127.0.0.1', 54320 )
-				expect {
-					described_class.connect( '127.0.0.1', 54320, "", "", "me", "xxxx", "somedb" )
-				}.to raise_error(PG::ConnectionBad, /server closed the connection unexpectedly/)
-			end
-
-			sleep 0.5
-			expect( t ).to be_alive()
-			serv.close
-			t.join
-		end
-	end
-
 	describe "type casting" do
 		it "should raise an error on invalid param mapping" do
 			expect{