Issue #582: disallow tabs before inline comments

[spaceone]

Detect invalid tabs before inline comments:

printf 'foo = "bar" \t# comment\n' | pycodestyle -
stdin:1:12: E261 at least two spaces before inline comment
printf 'foo = "bar"\t # comment\n' | pycodestyle -
stdin:1:12: E261 at least two spaces before inline comment
printf 'foo = "bar"\t\t# comment\n' | pycodestyle -
stdin:1:12: E261 at least two spaces before inline comment

Fixes #582

[spaceone]

any reviewers?

[asottile]

I don't think this is correct, a space + a tab is "at least two spaces"

[spaceone]

Hmm, I don't think so. Why should you mix tabs and spaces?
This is especially annoying in code, which wants to migrate from tabs to spaces - some leftover tabs aren't detected.

Alternatively can I introduce a new error for this?