MD5 hash of contents

[dannykopping]

Prevent modified files from being overwritten by having a hidden file in the services & VO folders containing MD5 hashes of the contents of each of the files. When Admin attempts to rewrite the file, check the hash and:

a) if no file exists, create one with all files' hashes
b) if no hash exists for the file, add it to the file
c) if a hash exists, compare it to the new hash:

• if they match, do nothing
• if they differ, offer a choice to the user to overwrite this file (or all subsequent files - "Yes to All")