FILTER_VALIDATE_INT should support FILTER_FLAG_ALLOW_THOUSAND

### Description

just like
```
filter_var("231,402,800",FILTER_VALIDATE_FLOAT, FILTER_FLAG_ALLOW_THOUSAND)
```
returns
```
float(231402800)
```
doing
```
filter_var("231,402,800",FILTER_VALIDATE_INT, FILTER_FLAG_ALLOW_THOUSAND)
```
should return
```
int(231402800)
```
rather than the current 
```
bool(false)
```