Performance tests cleanups

Performance tests cleanups

This patch brings the performance tests more up to date, by doing several
cleanups:

 - Fix the Makefile so it's more correct when building and linking.
 - Remove the streaming test, and rename the parallel test to performance.
   The streaming test is exactly the same test as the parallel with one
   thread, so why keep both around?
 - Fix some comments and minor style changes.
 - Expand the help.
 - Mark the functions and static data as static.
 - Use proper types (unsigned long, ssize_t) instead of int.
 - Add checks for the return of some calls like malloc().
 - The blocksize is now passed in Kb, to make it easier to use bigger
   sizes.
 - Do not open the file O_SYNC, it makes no sense.
 - Run jfsck after all the writes, and verify it went well.

Signed-off-by: Alberto Bertogli <albertito@blitiri.com.ar>