RT1325,2973: Add more extensions to c_rehash

Add .crt/.cer/.crl to the filenames parsed.

I also updated the podpage (since it didn't exist when
this ticket was first created, nor when it was re-created
seven years later).

Reviewed-by: Tim Hudson <tjh@openssl.org>
(cherry picked from commit 80ec8d4e3ee212786dc3092b1c97305b871827f0)