Since some days ago, upgrade of HEAD seems to be broken, due to some problems in the XMLDB definition of the "search" block. It seems that default values have been quoted and that produce double-quoting of generated SQL statements that use to crash.
Soution is to strip all those quotes from default values, XMLDB stuff will generate, then the proper SQL and PHP.
Also we could enhance the editor to warn about this type of values.
(assign to me if you want) Ciao