test: Switch to the new PRNG instead of old LCG

test: Switch to the new PRNG instead of old LCG

Wallclock time for running pixman "make check" (compile time not included):

----------------------------+----------------+-----------------------------+
                            | old PRNG (LCG) |   new PRNG (Bob Jenkins)    |
       Processor type       +----------------+------------+----------------+
                            |    gcc 4.5     |  gcc 4.5   | gcc 4.7 (simd) |
----------------------------+----------------+------------+----------------+
quad Intel Core i7  @2.8GHz |    0m49.494s   |  0m43.722s |    0m37.560s   |
dual ARM Cortex-A15 @1.7GHz |     5m8.465s   |  4m37.375s |    3m45.819s   |
     IBM Cell PPU   @3.2GHz |    23m0.821s   | 20m38.316s |   16m37.513s   |
----------------------------+----------------+------------+----------------+

But some tests got a particularly large boost. For example benchmarking and
profiling blitters-test on Core i7:

=== before ===

$ time ./blitters-test

real    0m10.907s
user    0m55.650s
sys     0m0.000s

  70.45%  blitters-test  blitters-test       [.] create_random_image
  15.81%  blitters-test  blitters-test       [.] compute_crc32_for_image_internal
   2.26%  blitters-test  blitters-test       [.] _pixman_implementation_lookup_composite
   1.07%  blitters-test  libc-2.15.so        [.] _int_free
   0.89%  blitters-test  libc-2.15.so        [.] malloc_consolidate
   0.87%  blitters-test  libc-2.15.so        [.] _int_malloc
   0.75%  blitters-test  blitters-test       [.] combine_conjoint_general_u
   0.61%  blitters-test  blitters-test       [.] combine_disjoint_general_u
   0.40%  blitters-test  blitters-test       [.] test_composite
   0.31%  blitters-test  libc-2.15.so        [.] _int_memalign
   0.31%  blitters-test  blitters-test       [.] _pixman_bits_image_setup_accessors
   0.28%  blitters-test  libc-2.15.so        [.] malloc

=== after ===

$ time ./blitters-test

real    0m3.655s
user    0m20.550s
sys     0m0.000s

  41.77%  blitters-test.n  blitters-test.new  [.] compute_crc32_for_image_internal
  15.77%  blitters-test.n  blitters-test.new  [.] prng_randmemset_r
   6.15%  blitters-test.n  blitters-test.new  [.] _pixman_implementation_lookup_composite
   3.09%  blitters-test.n  libc-2.15.so       [.] _int_free
   2.68%  blitters-test.n  libc-2.15.so       [.] malloc_consolidate
   2.39%  blitters-test.n  libc-2.15.so       [.] _int_malloc
   2.27%  blitters-test.n  blitters-test.new  [.] create_random_image
   2.22%  blitters-test.n  blitters-test.new  [.] combine_conjoint_general_u
   1.52%  blitters-test.n  blitters-test.new  [.] combine_disjoint_general_u
   1.40%  blitters-test.n  blitters-test.new  [.] test_composite
   1.02%  blitters-test.n  blitters-test.new  [.] prng_srand_r
   1.00%  blitters-test.n  blitters-test.new  [.] _pixman_image_validate
   0.96%  blitters-test.n  blitters-test.new  [.] _pixman_bits_image_setup_accessors
   0.90%  blitters-test.n  libc-2.15.so       [.] malloc