Ignore Eclipse project files
Make startup scripts whitespace-safe.

This is in preparation for future parameters which
may contain whitespaces.
Pacify C compiler

This eliminates a warning about a missing return
statement. The code was correct though, because
hex2num() is guarded by is_hexdigit().
Fix line indentation

This is purely cosmetic.
Support for multiple secrets

The secrets file is now parsed line by line, and
each line (excluding CR and/or LF) is used as a secret.
Only the first secret is used for signing, but all
secrets are used for verification.
Optionally exclude domains from address rewriting

Useful for subdomains which are handled by the same
mail server.