macros.

It does not fixes any bugs in 4.0. But it prevents from future error in
any bugfixes that may use these macros. Also after merging into 4.1 tree
this cleanup will fix bug #7884 "Able to add invalid unique index on
TIMESTAMP prefix".


sql/field.h:
  Since FIELDFLAG_INTERVAL, FIELDFLAG_BITFIELD, FIELDFLAG_BLOB and
  FIELDFLAG_GEOM flags occupy the same space as number of decimals for
  FIELDFLAG_NUMBER fields, it is safer to check in "f_is_geom()"-type
  macros that we have non-number field, like we already do in f_is_blob()
  macro.