Rename old crash cases to match the current naming scheme.

Will allow for easy import of crash cases from swift-compiler-crashes.

validation-test/compiler_crashers_fixed/00261-swift-parser-parseexprpostfix.swift

@@ -0,0 +1,15 @@
+// RUN: not %target-swift-frontend %s -parse
+
+// Distributed under the terms of the MIT license
+// Test case submitted to project by https://github.com/practicalswift (practicalswift)
+// Test case found by fuzzing
+
+func h(f: Int = j) {
+}
+let i = h
+i() -> f {
+    {
+    func e(#i: d, g: d) {
+        for f in h {
+            f.i(i, g)
+        } }