[Suggestion] Change indentation to one letter per indentation level.

Please change the indentation to one letter per indentation level.

bzr cat -d lp:calibre src/calibre/libwand.py|cat -A - illustrate the problem. A one letter indentation would be shown as "^I" but this show indentation as " ".

It's not clear if this is by intention or by mistake. In both cases it should be fixed.

Thanks!