Correction of multiple instance of wPaint

Hi,

this correction is needed to avoid to have an error in the path of menu's images after some instances of wPaint.

Indeed :
Initially, the items of $.fn.wPaint.menus have their img attribute set to "plugins/main/img/...". After the first initialization with "element.wPaint()", $.fn.wPaint.menus have their img attribute set to "<path>plugins/main/img/..."
If we have another page with wPaint, the path is set to "<path><path>plugins/main/img/..." (path is appended for each loading).

Thx.