scripts/sloccount: Pipe find stderr to /dev/null

This was causing the following error output:

    $ ./tools/sloccount
    find: cannot search ‘’: No such file or directory
    find: cannot search ‘’: No such file or directory
    find: cannot search ‘’: No such file or directory
    find: cannot search ‘’: No such file or directory
    find: cannot search ‘’: No such file or directory
    find: cannot search ‘’: No such file or directory
    find: cannot search ‘’: No such file or directory
    find: cannot search ‘’: No such file or directory
    find: cannot search ‘’: No such file or directory
    find: cannot search ‘’: No such file or directory
    find: cannot search ‘’: No such file or directory
    pip-db 0.2.2 - Source lines of code
    Tue Jan 14 18:06:34 GMT 2014

    Build system: 962
    find: cannot search ‘’: No such file or directory
       468  configure.ac       (48.65%)
       321  Makefile.am        (33.37%)
       173  autogen.sh         (17.98%)

    Resources: 7824
    find: cannot search ‘’: No such file or directory
    find: cannot search ‘’: No such file or directory
      7639  Less CSS           (97.64%)
       185  JavaScript         (2.36%)

    Sources: 2439
    find: cannot search ‘’: No such file or directory
    find: cannot search ‘’: No such file or directory
      1371  Clojure (tests)    (56.21%)
      1068  Clojure            (43.79%)

    Documentation: 28052
    find: cannot search ‘’: No such file or directory
    find: cannot search ‘’: No such file or directory
     27176  Markdown           (96.88%)
       876  LaTeX              (3.12%)

    Tools: 6752
    find: cannot search ‘’: No such file or directory
    find: cannot search ‘’: No such file or directory
    find: cannot search ‘’: No such file or directory
    find: cannot search ‘’: No such file or directory
      3848  Ruby               (56.99%)
      1516  JavaScript         (22.45%)
       921  Python             (13.64%)
       467  Shell              (6.92%)

    Total physical source lines of code: 46029