[php] Std.parseInt allows exponent notation

[tobil4sk]

While looking to fix some parseInt issues (PR soon), I noticed that Std.parseInt on php allows for the exponent notation.

Std.parseInt("10e2"); // returns 1000

This does not match the other targets, which treat the e2 as trailing text.

It may be best to document this as unspecified behaviour to avoid making the parseInt implementation too complex?