Add a bootstrap script for running rustfmt on itself.

bootstrap.sh

@@ -0,0 +1,18 @@
+#!/bin/bash
+
+# Make sure you double check the diffs after running this script - with great
+# power comes great responsibility.
+# We deliberately avoid reformatting files with rustfmt comment directives.
+
+cargo build
+
+target/debug/rustfmt --write-mode=overwrite src/lib.rs
+target/debug/rustfmt --write-mode=overwrite src/bin/rustfmt.rs
+target/debug/rustfmt --write-mode=overwrite src/bin/cargo-fmt.rs
+target/debug/rustfmt --write-mode=overwrite tests/system.rs
+
+for filename in tests/target/*.rs; do
+    if ! grep -q "rustfmt-" "$filename"; then
+        target/debug/rustfmt --write-mode=overwrite $filename
+    fi
+done