Ports/bash: Make a /bin/bash symlink to /usr/local/bin/bash

I've added a post_install step to the system that allows you to run
arbitrary commands after the regular install step.

This allows scripts that start with "#!/bin/bash" to work in Serenity.

Ports/bash/package.sh

@@ -14,3 +14,8 @@ build() {
     run_replace_in_file "s/define CAN_REDEFINE_GETENV 1/undef CAN_REDEFINE_GETENV/" config.h
     run make $makeopts
 }
+
+post_install() {
+    mkdir -p $SERENITY_ROOT/Root/bin
+    ln -s /usr/local/bin/bash $SERENITY_ROOT/Root/bin/bash
+}