Removing preloads from mains tests

Instead of loading all preload for all tests, adding just those functions that are needed for each. Should reduce test times.

Also renaming tests to give some indication of difficulty. Alas they are not run in that order.

test/mains/source/10_add__4.rb

@@ -0,0 +1,10 @@
+class Integer < Data4
+  def +(right)
+    X.int_operator(:+)
+  end
+end
+class Space
+  def main(arg)
+    return 2 + 2
+  end
+end