Not going to assume that $twitter is a URL
largo_twitter_url_to_username now ignores trailing slash and @
Trims Twitter URLs and @usernames to usernames, but only when invalid

The Twitter URL or @username is converted to a bare username when:

- the user is editing their own profile and
	- the new value's username contains a character not in the set `[a-zA-Z0-9_]`
- the user is editing another user's profile and
	- the new value's username contains a character not in the set `[a-zA-Z0-9_]`

It is not converted when:

- the user is editing their own profile and
	- the new value is of the form `http://twitter.com/username`
	- the new value is of the form `https://twitter.com/username`
	- the new value is of the form `http://twitter.com/@username`
	- the new value is of the form `https://twitter.com/@username`
	- the new value is of the form `twitter.com/username`
	- the new value is of the form `twitter.com/@username`
	- the new value is of the form `http://plus.google.com/username`
- the user is editing another user's profile and
	- the new value is of the form `http://twitter.com/username`
	- the new value is of the form `https://twitter.com/username`
	- the new value is of the form `http://twitter.com/@username`
	- the new value is of the form `twitter.com/username`
	- the new value is of the form `twitter.com/@username`
	- the new value is of the form `http://plus.google.com/username`
move var_log to helpers.php
This works, but writing to $_POST seems inadvisable

I don't know why it seems inadvisable, and I can't find anything saying
not to do it, so here we go.
Merging develop branch back in
tests for largo_twitter_url_to_username and the edit submission twitter cleanup hooks
Fixing broken tests
Now lets through everything that's not a URL parameter, even if invalid character #gotests
letting the users know they have options
Close the <em>tags<em> that were left hanging, like so
Updates sticky footer for new user twitter username save
Fixing the post-tags.php tweet button data-related
Merge pull request #305 from INN/improved-twitter-username-function

Improved twitter username function for #270