Directories should be locked

[bugdea1er]

To prevent deletion from another program and the same vulnerability we prevented in #165, the temporary directory should be locked to prevent an attacker from replacing its path with a symlink

• NTFS supports atomic mandatory locking when using CreateFile
• Some Linux systems support mandatory locking for tmpfs
• At the very least, advisory locking should be added to all systems, as discussed here

[bugdea1er]

Memory was reserved in directory in #190 to store the directory handle