Fix signature computation in compile_extension_module.

Add instant_kwargs to signature. Fixes this bug:

from dolfin import *
m2 = compile_extension_module('', cppargs='-O2')
m3 = compile_extension_module('', cppargs='-O3')
assert(m2.__file__ != m3.__file__)
Add test for instant_kwargs compile_extension_module fix.
No need to check -O3 in this ad hoc test.

-O2 is ok as it is Instant's default.
Changed print to print() and used print_ for soft spaces, changed d.values() to list(d.values()) and d.iteritems() to six.iteritems(d)
Automatically generated.
Automatically generated code
Changes syntax for except, has_key, raise and reduce
Changed isinstance
Changed long, map and  metaclass
Changed it.next() with six.advance_iterator(it)
Changed range and xrange
Change types
Add __future__ print and remove double parentheses in print statements
Find correct swig
Find correct python
New C API syntax
Python 3 syntax
Change due to python 3 C API
Relative import and pyton 3 syntax
Make dolfin find correct python