fix semisync plugins and tests to work with both with static and dynamic linking

MySQL 5.1 and 5.2 alpha trees.

avoid unnecessary strlen()'s

(but support the scopeless mysql style too).
always output status/system variables in the correct lettercase

and INFORMATION_SCHEMA.ALL_PLUGINS table
with condition pushdown for I_S.ALL_PLUGINS
and a  new status variable to cound successful dlopen's

Change Item_func_get_system_var::val_xxx functions to use that.

mysql-test/t/variables.test:
  @@GLOBAL.INIT_CONNECT is never NULL anymore. Nor it ever was.
  It was a bug that empty string system variables appeared as NULL
  in the *integer context* (but not in a string, real, or decimal context!)

instead of "used storage engine" and similar changes.

implement ./mtr --dry-run

not part of the SE API, and, again, mutually exclusive with
C_ORDINARY_CREATE and C_CREATE_SELECT.

allocated by the same allocator as in TABLE_SHARE::read_frm_image()

eliminating reduncancy and a possibility of setting them to a pair of
invalid values.

* persistent table versions in the extra2
* ha_archive::frm_compare using TABLE_SHARE::tabledef_version
* distinguish between "important" and "optional" extra2 frm values
* write engine-defined attributes (aka "table options") to extra2, not to extra,
  but still read from the old location, if they're found there.

use it to test main test cases with need_full_discover_for_existence > 0

Now CREATE TABLE does not write the frm file on disk,
if the engine can discover it

(in partition_archive.test frm size goes down 16 times :)

(allocating and freeing buffers on the way), allocate
one frm buffer, prepare the frm image completely in memory,
and then write it down.

* comments
* cosmetic changes, *(ptr+5) -> ptr[5]
* a couple of trivial functions -> inline
* remove unused argument from pack_header()
* create_frm() no longer creates frm file (the function used to prepare and
  fill a memory buffer and call my_create at the end. Now it only prepares
  a memory buffer). Renamed accordingly.
* don't call pack_screen twice, go for a smaller screen area in the first attempt
* remove useless calls to check_duplicate_warning()
* don't write unireg screens to .frm files
* remove make_new_entry(), it's basically dead code, always calculating
  and writing into frm the same string value. replace the function call
  with the constant string.

from everywhere - now RENAME, SHOW FULL TABLES, and TRUNCATE work with discovery.
improve error messages in truncate