FIX: SUPPLIER_PROPOSAL_FREE_TEXT get HTML tags removed

[warnerbryce]

FIX

on the admin page of Supplier Proposal,
You have an Fckeditor frame where you can set the const SUPPLIER_PROPOSAL_FREE_TEXT
Compared to other FREE_TEXT on other modules, this one get preg_match before writing into database.
The problem is that the GETPOST function remove the HTML TAGS of the text entered.
You will get a bad looking text when printing onto PDF.

I corrected the GETPOST function to put the argument check on restrickhtml.

EDIT :
There is others CONSTANTS to write into database on this page, so i made the GETPOST modification just for SUPPLIER_PROPOSAL_FREE_TEXT