Good for a 10-15% speedup

I still feel like we can do much better here though

(Committed by kmod)
Closes #93

Make check_format actually useful

Add sudo for zsh installation

Property

Some small changes to simplify the generated IR.

Also make a note that the CPython development headers are necessary
for running the tests.

Fix typo in IOError format string

This fixes an annoying typo introduced in cfe83db0.

+ mark the alloc routines as no alias (=attribute(malloc)).
  This marks every alloc call as noalias in the IR.
  (While I felt somewhat frightened by the malloc attribute AFAIK the generated IR looks reasonable.)
+ inline the trivial Box constructor
+ fix dead allocs pass: we will now remove the useless list creation inside f2 in speculation_test.py

Small improvements for file objects.