Fix some bugs :

Fix some bugs :
* worked in 1.9.0, but not in 1.9.1 :
- modif of a biblio didn't work
- empty fields where not shown when modifying a biblio. empty fields managed by the library (ie in tab 0->9 in MARC parameter table) MUST be entered, even if not presented.

* did not work before :
- repeatable subfields now works correctly. Enter 2 subfields separated by | and they will be splitted during saving.
- dropped the last subfield of the MARC form :-(

Internal changes :
- MARCmodbiblio now works by deleting and recreating the biblio. It's not perf optimized, but MARC is a "do_something_impossible_to_trace" standard, so, it's the best solution. not a problem for me, as biblio are rarely modified.
Note the MARCdelbiblio has been rewritted to enable deletion of a biblio WITHOUT deleting items.