Add ARCHIVES_DIR variable pointing to directory containing the source archives.
Shorten commit messages.

Only mention the TrueCrypt version and whether the change came from the ZIP file for Windows.

Shortening the message gives the version more visibility when for example using blame.
Extract tar.gz source archives before the zip ones.

Reduces the number of commit messages referencing "Windows" because (most) file changes in a new version that is extracted will now come from the tar.gz archive.
Slightly change the commit message.