Fix some warnings

Add new module_FindName function to find a module when given it's name. Use this to fix the qt interface extended panel (video filters).
Change module_Exists to take the module name (and not short name) as parameter. Update the only known use of that function acordingly.

Enforce access to input_item_t through input_item_{G,S}et*()
Unlock mutexes before calling these functions
Free strings returned by input_item_Get*()

New functions added:

char * input_item_GetURI( input_item_t  * )
void input_item_SetURI( input_item_t * , char * )

mtime_t input_item_GetDuration( input_item_t * )
void input_item_SetDuration( input_item_t * , mtime_t )

to access input_item_t->psz_uri and input_item_t->i_duration

Revert [21140] which broke the extend panels in Qt4 + add a comment so this doesn't happen again. (Please test changes before commiting ... thanks)

control/media_list.c: Revert the tagging of the subitems. This is not our job. Also not add the subitems to our list. We need a new media_tree object that will handle that itself.

 - specify server_port and, if needed, source
 - check for unsupported options
 - use proper default values
 - try transport successively until one works (untested!)

 - "handle" Require header
 - return 459/460 when appropriate