Fix OptInt's valid?() function

[FixRM #7539] - The valid?() function will first normalize() the
user-supplied input before validation.  The problem is that the
normalize() function will ALWAYS convert data to integer, therefore
whatever you validate, you will always get true.  For example:
when I do "yomama".to_i, that returns 0, and of course will pass
integer validation.
Merge pull request #1293 from wchen-r7/optint_valid

Fix OptInt's valid?() function