MEDIUM: pools: better check for size rounding overflow on registration

MEDIUM: pools: better check for size rounding overflow on registration

Certain object sizes cannot be controlled at declaration time because
the resulting object size may be slightly extended (tag, caller),
aligned and rounded up, or even doubled depending on pool settings
(e.g. if backup is used).

This patch addresses this by enlarging the type in the pool registration
to 64-bit so that no info is lost from the declaration, and extra checks
for overflows can be performed during registration after various rounding
steps. This allows to catch issues such as these ones and to report a
suitable error:

  global
      tune.http.logurilen 2147483647

  frontend
      capture request header name len 2147483647
      http-request capture src len 2147483647
      tcp-request content capture src len 2147483647