Remove number_format() call from "is overloaded" comparison - it returns a string, which compares by string sorting instead of numeric order

This is a problem when "overload" is an order of magnitude lower than the value
(e.g. overload is 900, value is 1000, number_format returns 1,000.00, string comparison sorts 1 before 9, so says that there isn't an overload)
Doing maths on a string (the division) makes PHP try to parse it as a number (which it is) and we get numeric comparison, where 1000 > 900
Replace number_format() with type casting in Apache graph to prevent string comparison

As per change in Memory graph, if the value is an order of magnitude larger but the first digit is smaller
(e.g. 10 vs 7: 10 > 7 but 1 < 7) then string comparisons will give the wrong answer, and number_format gives a string
Merge pull request #11 from IBBoard/overload-fix

Overload fix