specific
- adding TRN::first_undo_lsn, needed to know when a log can be deleted;
this variable must be set under log's mutex and that leads to setting
TRN::rec_lsn, TRN::undo_lsn and TRN::first_undo_lsn in a
inwrite_rec_hook; adding implementation of one hook for REDOs and one
for UNDOs. Thus translog_write_record() always uses TRN and so does
not need a short_id argument, can find it from TRN.
- Monty's patch for the last Valgrind error in the tree.
- Log handler's unit tests fail but Sanja says it's known


include/Makefile.am:
  pagecache.h moved and renamed
include/maria.h:
  pagecache.h moved and renamed
sql/handler.h:
  pagecache.h moved and renamed
storage/maria/Makefile.am:
  pagecache.h moved and renamed
storage/maria/ha_maria.cc:
  adding an assertion which sounds logical
storage/maria/ma_blockrec.c:
  trn->rec_lsn and trn->undo_lsn are now set via hooks inside the log
  record's writing; this allows to also set trn->first_undo_lsn
  needed to compute the log's low-water mark.
  The PAGERANGE_STORE_SIZE -> PAGE_STORE_SIZE is Monty's fix to a
  Valgrind error.
storage/maria/ma_loghandler.c:
  "tcb" renamed to "trn". Log handler now knows what is a transaction,
  and finds short_id from trn. trn's rec_lsn, undo_lsn, first_undo_lsn
  are now set by some inwrite_rec_hookS (one for REDOs, one for UNDOs).
  The HAVE_purify blocks are Monty's fix to a Valgrind error.
storage/maria/ma_loghandler.h:
  Log handler functions use TRN, that needs a forward declaration
storage/maria/ma_pagecache.c:
  pagecache.h was moved and renamed
storage/maria/ma_pagecache.h:
  pagecache.h was moved and renamed
storage/maria/ma_pagecaches.c:
  pagecache.h was moved and renamed
storage/maria/trnman.c:
  initializing some members of TRN.
storage/maria/trnman.h:
  TRN::first_undo_lsn needed for log's low-water mark calculation
  (which will serve to know which logs can be deleted)
storage/maria/unittest/ma_test_loghandler-t.c:
  translog_write_record() now needs a valid TRN
storage/maria/unittest/ma_test_loghandler_multigroup-t.c:
  translog_write_record() now needs a valid TRN
storage/maria/unittest/ma_test_loghandler_multithread-t.c:
  translog_write_record() now needs a valid TRN
storage/maria/unittest/ma_test_loghandler_pagecache-t.c:
  translog_write_record() now needs a valid TRN
storage/maria/unittest/test_file.h:
  pagecache.h was moved and renamed