Make normalize_whitespace faster

[pictuga]

This had significant consequences on a program of mine.

Before:

real    0m5.776s
user    0m4.150s
sys 0m0.077s

After:

real    0m4.261s
user    0m4.130s
sys 0m0.073s

(That's more than a second difference!)

(breadability is called on ± 30 pages during my script execution)

This drops the distinction between \n and whitespaces, but from what I've understood, this distinction is actually not used in the code after.

[miso-belica]

I think you should look at user time.

And your solution doesn't preserve new lines which may be significant for someone (e.g. for me :). It's great to have code fast but it should work in the first place :)