Calculate the integer logarithm for an arbitrary base.
The base must be greater than
1, the second argument, the
number whose logarithm is sought, shall be positive, otherwise the
result is meaningless.
The following property holds
base ^ integerLogBase# base m <= m < base ^(integerLogBase# base m + 1)
for
base > 1 and
m > 0.
Note: Internally uses
integerLog2# for base 2