MIsc improvements

Bugfixes

 *  Allow optional file paramaters 97353c5
 *  Discard heuristics of 'novel' injections in shared sections 4ea289b
 *  Allow multiple failing enclosed values for Eliom_parameter.{opt,neopt} cc6a42d

Additions

 * string_radio_required and option required for select 	3328046
 * Type of event handlers consistently on server and client	059b742
 * Add required option to select element 	af4929d
 * Export Eliom_client.form_handler for hacking eliom forms from outside 	dba2f08

Tools

 * Use -ppopt files in eliomdep 	7cc05bb
 * Use -ppopt arguments in eliomc also for ml/mli files 	46667ea