[FIX] ir_values: try to evaluate the given expression before saving it in pickle...

[FIX] ir_values: try to evaluate the given expression before saving it in pickle form (opw 607398)

The value_unpickled given by xml data is usualy already evaluated but when it is given by the web client, a str is recieved by the method (as the field is a text field). In the later case, we need to evaluate the field before storing to be correctly evaluated as a default value.

bzr revid: mat@openerp.com-20140509130412-ki211x7qdccdnv5w