Indentation - tabs include some preceding spaces

The indentation fix assumes that a tab is just 4 spaces - rather than an indentation to the next multiple of 4 spaces.

For example, in an editor, the following would look identical:

    <space><space><space><space>FOO
    <space><space><space><tab>FOO
    <space><space><tab>FOO
    <space><tab>FOO
    <tab>FOO

The existing code would fix it as

    <space><space><space><space>FOO
    <space><space><space><space><space><space><space>FOO
    <space><space><space><space><space><space>FOO
    <space><space><space><space><space>FOO
    <space><space><space><space>FOO

This new code would fix it as

    <space><space><space><space>FOO
    <space><space><space><space>FOO
    <space><space><space><space>FOO
    <space><space><space><space>FOO
    <space><space><space><space>FOO