Fixes getter methods created when plugins are initialized.

[deefour]

Because the following function definition is not wrapped in a closure

self[name] = function() { return plugin; };

plugin's scope is the TextExt.initPlugins function. Because of this,
on each iteration of the list of plugins to create the getter methods in
TextExt, the return value of all created methods will be the last
value of plugin and not the value of plugin from when the function
was defined for each.

Wrapping the function definition in a closure fixes this issue.

As an explicit example:

Previously, when instantiating a new textext(...) instance and
defining the plugins option as

plugins: 'autocomplete arrow'

All 3 of the following would return the TextExtArrow instance

$('...').textext()[0].ie9();
$('...').textext()[0].autocomplete();
$('...').textext()[0].arrow();

After they closure from this changeset is applied, they return their
expected plugin instances

 $('...').textext()[0].ie9();          // TextExtIE9Patches
 $('...').textext()[0].autocomplete(); // TextExtAutocomplete
 $('...').textext()[0].arrow();        // TextExtArrow

[alexgorbatchev]

Thank you!