Adding benchmark_disks_random to stxxl_tool.
Moving mlock and mallinfo tools into stxxl_tool.
Merging functionality of verify_disks into stxxl_tool benchmark_files subtool.
Removing flushbuffers and gen_file tool, because they are obsolete by benchmark_files and create_files subtools.
Moving sd_test into test_sim_disk.cpp.
Reorganise tools into extras/ and benchmarks/.
Enabling compilation of old benchmarks using TPIE and BerkeleyDB if these are found.
Conditional compilation options for mlock and mallinfo, further changes to fix test runs on Windows.