Consolidate duplicate definitions

Consolidate duplicate definitions

Housekeeping change to consolidate some common definitions.
Create a new common header called afs_consts.h.  This allows
us to remove the afscp.c dependency on afs.h (so src/tests
will build again.) Rename the max filename definition in the
update server package to MAXFNSIZE to avoid a name conflict
with MAXSIZE.  The global defines will be prefixed with
AFS_ in a second patch.

Change-Id: I2b8d555a244cc92d889618de4eec4a99550d7c7f
Reviewed-on: http://gerrit.openafs.org/855
Reviewed-by: Mickey Lane <mlane@sinenomine.net>
Tested-by: Mickey Lane <mlane@sinenomine.net>
Reviewed-by: Derrick Brashear <shadow@dementia.org>
Tested-by: Derrick Brashear <shadow@dementia.org>