Adding three new parameters with safe defaults

always_add_missing_headers, mailbox_size_limit, transport_maps.  Only add
them if the user specifies at all.

I don't have an el6 machine to test this on.  I made the changes there as
well since they don't overlap anything, but it could be bad, I don't know.
Removing spurious whitespace in template

It doesn't matter, but the previous change added three empty lines at the end of
my file.  Eh.
Adding four new parameters for SSL

* ssl_key: the path to the SSL key for the server
* ssl_cert: the path to the cert (with any chain) for the server
* ssl_ca: the path to the CA file
* ssl_create_dh: if set, will generate the DH parameter files for the
                 server
Typo in server.pp. :(
Copying my main.cf.erb changes into the EL6 one
Revert "Copying my main.cf.erb changes into the EL6 one"

This reverts commit 9a3b1fc759518db5e249248536f4a6c1e9001978.
Sometimes you've got to set inet_protocols.  :(
fallback_relay->smtp_fallback_relay on > 2.2

2.2 is really old, y'all
Merge branch 'update-fallback' into add-parameters
Revert "Merge branch 'update-fallback' into add-parameters"

This reverts commit 910f03a55cb3640fba69622fe53f74377fed209d, reversing
changes made to 304d7f3bfc5d56d1bb7470f7df015e39718fa627.

I realized we don't want this merged in here, it'll make things harder to
merge into master later.