Added count of my_sync calls (to SHOW STATUS)

tmp_table_size can now be set to 0 (to disable in memory internal temp tables)
Improved speed for internal Maria temp tables:
- Don't use packed keys, except with long text fields.
- Don't copy key all accessed pages during key search.
Some new benchmark tests to sql-bench (for group by)

BUILD/compile-pentium64-gcov:
  Update script to use same pentium_config flags as other tests
BUILD/compile-pentium64-gprof:
  Update script to use same pentium_config flags as other tests
include/my_sys.h:
  Added count of my_sync calls
mysql-test/r/variables.result:
  tmp_table_size can now be set to 0
sql-bench/test-select.sh:
  Added some new test for GROUP BY on a not key field and group by with different order by
sql/mysqld.cc:
  Added count of my_sync calls
  tmp_table_size can now be set to 0 (to disable in memory internal temp tables)
sql/sql_select.cc:
  If tmp_table_size is 0, don't use in memory temp tables (good for benchmarking MyISAM/Maria temp tables)
  Don't pack keys for Maria tables;  The 8K page size makes packed keys too slow for temp tables.
storage/maria/ma_key_recover.h:
  Moved definition to maria_def.h
storage/maria/ma_page.c:
  Moved code used to simplify comparing of identical Maria tables to own function (page_cleanup())
  Fixed that one can read a page with a read lock.
storage/maria/ma_rkey.c:
  For not exact key reads, cache the page where we found key (to speed up future read-next/read-prev calls)
storage/maria/ma_search.c:
  Moved code to cache last key page to separate function.
  Instead of copying pages, only get a link to the page. This notable speeds up key searches on bigger tables.
storage/maria/ma_write.c:
  Added comment
storage/maria/maria_def.h:
  Moved page_cleanup() to separate function.

mysql-test/r/variables.result

@@ -575,8 +575,6 @@ set storage_engine=myisam;
 set global thread_cache_size=100;
 set timestamp=1, timestamp=default;
 set tmp_table_size=100;
-Warnings:
-Warning	1292	Truncated incorrect tmp_table_size value: '100'
 set tx_isolation="READ-COMMITTED";
 set wait_timeout=100;
 set log_warnings=1;