clrs; exercise 8.4.1 - illustrate BUCKET-SORT
clrs; exercise 8.4.2 - why is worst-case Θ(n²)
clrs; exercise 8.4.3 - E[X] for head in 2 coins
clrs; exercise 8.4.4 - bucket-sort points in 1-circle
clrs; exercise 8.4.5 - bucket-sort prob dist fn
clrs; improve the pre-commit-msg hook

* Don't do anything if commit already contains a message. This is
  required because fugitive otherwise prints the message twice
* Use emulate -LR to be less fragile
* Simplify the check if all files have the same prefix