Moving the test_pagecache_ tests from mysys to unittest/mysys.
Means fixing includes to work with the new directory, some Makefile.am
editing, replacing memset() with bfill().
test_page_cache_*.c renamed to mf_pagecache_*-t.c (-t is the standard
suffix for tests in the mytap protocol).
Also added plan() and exit_status() calls to tests.
Sanja, I put some TODOs for you at the start of mf_pagecache_*.c


unittest/mysys/test_file.h:
  Rename: mysys/test_file.h -> unittest/mysys/test_file.h
mysys/Makefile.am:
  pagecache test files move to top/unittest/mysys
mysys/mf_pagecache.c:
  my_bit.h needed to compile.
unittest/mysys/Makefile.am:
  INCLUDES is a better place for includes than AM_CPPFLAGS (the latter
  get overriden by prog_CPPFLAGS, which is not desirable here).
  Adding pagecache's test programs (moved from mysys);
  test_pagecache_* has been renamed to mf_pagecache*-t
  (-t is the required suffix for test executables in the mytap framework).
unittest/mysys/mf_pagecache_consist.c:
  fixing includes to work with the new directory.
  The test must return an exit code informing if any part failed.
  TODOs for Sanja.
unittest/mysys/mf_pagecache_single.c:
  fixing includes to work with new directory.
  adding a plan() to account for the number of tests.
  Adding exit_status() to tell how many tests failed.
  memset() was giving a compilation warning (implicit declaration etc),
  properly due to me removing stdio.h etc, so I replaced it with bfill().
  TODOs for Sanja.
unittest/mysys/test_file.c:
  moved from mysys (piece of the page cache tests) and includes fixed.