Removing primes.txt file, and applying some bash kung-fu to primes.sh

.gitignore

@@ -31,6 +31,7 @@ test_*
 qa
 gen
 unittest
+primes.txt
 
 # latex-generated files.
 book/*.pdf

src/apps/primes.sh

@@ -1,8 +1,6 @@
-#!/bin/bash
+#!/bin/sh
 
-cd `dirname $0`/../../
-
-cat /dev/null > primes.txt
+> primes.txt
 
 for i in {1..16}
 do