PEP8 whitespace cleanup

Warnings fixed:
devel/linkcheck:73:1: E305 expected 2 blank lines after class or function definition, found 1
wafhelpers/waf.py:29:5: E306 expected 1 blank line before a nested definition, found 0
wafhelpers/pythonize-header:84:1: E305 expected 2 blank lines after class or function definition, found 1
tests/wscript:38:1: E101 indentation contains mixed spaces and tabs
tests/wscript:38:1: W191 indentation contains tabs
tests/wscript:38:3: E131 continuation line unaligned for hanging indent
tests/wscript:39:1: E101 indentation contains mixed spaces and tabs
wscript:913:1: E305 expected 2 blank lines after class or function definition, found 1
wscript:949:1: E305 expected 2 blank lines after class or function definition, found 1
contrib/ntpheatusb:130:1: E305 expected 2 blank lines after class or function definition, found 1