Deprecated. Don't use for new development and try to migrate existing uses.
This function can be used to check if a given string is formally an integer, i.e. if the string contains only digits with an optional leading plus och minus character.
The special case of a null-string will give a return value of 0.
This function should NOT be used when determining whether a conversion to int or bigint is possible since it does not perform any overflow check. In these cases you should use the functions ADMIN_IsInt or ADMIN_IsBigint instead.
Returns 1 if the string is formally an integer and 0 otherwise.