dump_data() issues

[divergentdave]

I tried parsing a corrupt PDF file, and the program panicked with the following error. The unwrap() was in dump_data().

thread '<unnamed>' panicked at 'called `Result::unwrap()` on an `Err` value: Custom { kind: NotFound, error: PathError { path: "/tmp/pdf/oTRQva", err: Os { code: 2, kind: NotFound, message: "No such file or directory" } } }', src/libcore/result.rs:999:5

After I created a /tmp/pdf directory, the panic went away. However, since I didn't have logging on, it created a file in /tmp/pdf without notifying me of its presence. I'd recommend two changes to this function:

• Instead of specifying a subdirectory, use the OS's default directory, and provide a file name prefix like pdf-
• Only write files out when an environment variable is set, and log a message with instructions on setting the environment variable to dump the buffer if the environment variable is not set

[s3bk]

it will now only write if you set PDF_OUT to a directory.

[divergentdave]

Sounds good, thanks!