faster perfcurve (just in case you use FPR and TPR)

This version is identical to the one provided by matlab with a small change if "FPR" or "TPR" are used for X and Y.
Instead of using the tedious "arrayfun" I used vector cumsum functions.

Here is a test for comparison
N = 1e5;
score = [rand(N,1); rand(N,1)-1];
label = [ones(N,1); zeros(N,1)];

tic;
perfcurve(label, score, 1);
toc
tic;
perfcurve2(label, score,1);
toc

Elapsed time is 17.614076 seconds.
Elapsed time is 0.164707 seconds.

I hope you will find it useful.