Implement condition- and branching-free version of binmat_are_identical()

[devkev]

As noted in the source:

// Depending on the size of the matrices involved, and the depth of  
// pipelining on the arch we're running on (since conditional branching  
// destroys pipelining gains), it may be faster to just XOR the entire  
// matrices (with final masks) together, ORing against a "running result"  
// as we go.  The NOT of the running result is then the final result.  So  
// this way no conditionals or comparisons are required, and it amounts to  
// just streaming through memory doing fast bitwise operations.  

So, implement this (since it shouldn't be hard) and then run some benchmarks to see if it's worth keeping, and when.