Current master unit test errors

[Robert Stepanek]

I'm preparing a pull request for the master branch and noticed that
`make check` on a clone of the xapian repository fails badly. I haven't
merged my changes and built from e24cc6018de0. Is is just me or is there
something broken in the master branch?

    Running test './apitest' under valgrind
    Running tests with backend "none"...
    Running test: defaultctor1... SIGSEGV at (nil)
    DecreasingValueWeightPostingSource()
    [...]
    Running test: uninitdb1... InvalidArgumentError: Can't make an
    Enquire object from an uninitialised Database object.
    Running test: rset4... FAILED
    Running test: valuesetmatchdecider1... FAILED
    Running test: emptymset1... InvalidOperationError: Can't get
    termfreq from an MSet which is not derived from a query.
    Running test: nonutf8docdesc1... FAILED
    Running test: orphaneddoctermitor1... Invalid read of size 8
    Running test: serialise_query2... SIGSEGV at (nil)
    Running test: serialise_query3... SIGSEGV at (nil)
   ./apitest backend none: 134 tests passed, 9 failed.

Cheers,
Robert