websrv_lib: fix do_OPTIONS for m$ webdav
websrv_lib: fix do_OPTIONS for m$ webdav

Since we have moved all code into the websrv_lib, we must also support
this non-standard extension in our do_OPTIONS(). It has been noted that
some Win XP machines wouldn't connect to our WebDAV unless we set that
header.

splbio/openobject-server,MarkusTeufelberger/openobject-server,gisce/openobject-server,vnc-biz/openerp-server,gisce/openobject-server,ovnicraft/openerp-server,MarkusTeufelberger/openobject-server,MarkusTeufelberger/openobject-server,ovnicraft/openerp-server,splbio/openobject-server,splbio/openobject-server,gisce/openobject-server,vnc-biz/openerp-server