TempAlloc review starts now

[simendsjo]

I have very limited experience with D and haven't taken the time to understood the code, but here are
some easy nitpicks :)
----
imports: Should stuff in core really depend on phobos? Isn't much of the reason for core to allow
different "standard" libraries like tango?

177: should 16 be alignBytes?
199/299: unnecessary initializers
246: Move inUse.destroy() up to clearing of inUse?
291: Move assumption comment to assertion. Something like this:

bool isPowerOf(int pow, int num) {
    if(num <= 0 || pow <= 0)
        return false;
    else if(pow == 1)
        return true;
    else if(pow == num)
        return true;
    else {
        double n = cast(double)num / cast(double)pow;
        if(n%1 != 0)
            return false;
        else if(n == pow)
            return true;
        else
            return isPowerOf(pow, cast(int)n);
    }
}
unittest {
    static assert(isPowerOf(1, 0) == false); // num==0
    static assert(isPowerOf(1, 5) == true);  // pow==1
    static assert(isPowerOf(3, 3) == true);  // pow==num
    static assert(isPowerOf(2, 2) == true);
    static assert(isPowerOf(2, 3) == false);

    static assert(isPowerOf(2, 4) == true);
    static assert(isPowerOf(2, 1024) == true);
    static assert(isPowerOf(2, 1023) == false);
}

and in getAligned:
static assert(isPowerOf(2, alignBytes), "getAligned requires alignBytes to be a power of 2")

383/408/418/428: getState called without () (deprecated behavior, right..?)
686: missing () (same as above)