Add regression tests for obsolete issues

#KT-2592 Obsolete
 #KT-2768 Obsolete

compiler/testData/codegen/box/primitiveTypes/kt2768.kt

@@ -0,0 +1,17 @@
+fun assertEquals<T>(a: T, b: T) {
+    if (a != b) throw AssertionError("$a != $b")
+}
+
+fun box(): String {
+    val bytePos = 128.toByte() // Byte.MAX_VALUE + 1
+    assertEquals(-128, bytePos.toInt()) // correct, wrapped to Byte.MIN_VALUE
+
+    val shortPos = 32768.toShort() // Short.MAX_VALUE + 1
+    assertEquals(-32768, shortPos.toInt()) // correct, wrapped to Short.MIN_VALUE
+
+    assertEquals((-128).toByte().toString(), "-128")
+    // TODO: KT-2780
+    // assertEquals((-128.toByte()).toString(), "-128")
+
+    return "OK"
+}

compiler/testData/codegen/box/strings/kt2592.kt

@@ -0,0 +1,4 @@
+fun box(): String {
+    String()
+    return String() + "OK" + String()
+}