scripts/fsrefs: Fix -v

For this script verbose mode was added in 57bca1f0 (Add -v option to
control whether tracebacks are printed.) and was later broken in
6dd809d2 (Converted to a buildout and converted externals to
dependencies.) - the change forgot to add global specifier for VERBOSE
variable while moving its assignment into function context.

As a result currently we have

    $ python ./src/ZODB/scripts/fsrefs.py -v data.fs
    Traceback (most recent call last):
      File "./src/ZODB/scripts/fsrefs.py", line 155, in <module>
        main()
      File "./src/ZODB/scripts/fsrefs.py", line 104, in main
        VERBOSE += 1
    UnboundLocalError: local variable 'VERBOSE' referenced before assignment

Fix it.
scripts/netspace: Fix so it runs

Currently that script does not run because of import error:

    $ python src/ZODB/scripts/netspace.py
    Traceback (most recent call last):
      File "src/ZODB/scripts/netspace.py", line 13, in <module>
        from ZODB.referencesf import referencesf
    ImportError: No module named referencesf

and that ZODB.referencesf module was moved to ZODB.serialize long ago in

    ec014812    (Move referencesf to ZODB.serialize.)
    ae7e113e    (Ack!  Deleted the wrong file in the last checkin.)
    355ff4ac    (One more try.  Commit the version with referencesf.)

only the conversion missed the netspace.py script.

Fix it.
scripts/fsrefs: De-globalify verbose

As noted in recent commit, verbose option handling in fsrefs.py was
broken. On review Tres suggested to make VERBOSE a local variable as
currently it is used only in one function main().

Suggested-by: Tres Seaver
Merge pull request #25 from navytux/fixup

Small fixups while learning ZODB