indent(1): Fix indent's confusion about custom FreeBSD macros.

Teach indent(1) about storage-class specifiers. Don't assume
"in_parameter_declaration" state if "in_decl" hasn't been set. Don't set
"in_decl" for storage-class specifiers.

That set of changes helps with recognizing the difference between file
scope declarations like this:

static LIST_HEAD(, alq) ald_active;
static int ald_shuttingdown = 0;
struct thread *ald_thread;

and old style function declarators like this:

static int
do_execve(td, args, mac_p)
struct thread *td;
struct image_args *args;
struct mac *mac_p;
{

Unfortunately, at the same time this change makes indent(1) require
explicit int in declarations like "static a;", in order to understand that
it's part of a declaration. On the other hand, declarations like in the
first example are no longer indented as if ald_shuttingdown and ald_thread
were parameters of a function named LIST_HEAD.

Submitted by: Piotr Stefaniak