is_int that are used by FacebookException is too strict

Even if $result ['error_code']  is natural number, it might be string.
is_int so return true if and only if the type of a variable is integer, the decision I think this is one of the too strict.

#### Now (is_int)

value | return
------------- | -------------
0 | true
'0' | false
500 | true
'500' | false
'001' | false
'not int' |  false

#### Fixed (my preg_match check)

value | return
------------- | -------------
0 | true
'0' | true
500 | true
'500' | true
'001' | false
'not int' |  false