Table definition cache, part 2

The table opening process now works the following way:
- Create common TABLE_SHARE object
- Read the .frm file and unpack it into the TABLE_SHARE object
- Create a TABLE object based on the information in the TABLE_SHARE
  object and open a handler to the table object

Other noteworthy changes:
- In TABLE_SHARE the most common strings are now LEX_STRING's
- Better error message when table is not found
- Variable table_cache is now renamed 'table_open_cache'
- New variable 'table_definition_cache' that is the number of table defintions that will be cached
- strxnmov() calls are now fixed to avoid overflows
- strxnmov() will now always add one end \0 to result
- engine objects are now created with a TABLE_SHARE object instead of a TABLE object.
- After creating a field object one must call field->init(table) before using it

- For a busy system this change will give you:
 - Less memory usage for table object
 - Faster opening of tables (if it's has been in use or is in table definition cache)
 - Allow you to cache many table definitions objects
 - Faster drop of table

mysql-test/r/ndb_bitfield.result

@@ -201,18 +201,18 @@ create table t1 (
 pk1 bit(9) not null primary key,
 b int
 ) engine=ndbcluster;
-ERROR HY000: Can't create table './test/t1.frm' (errno: 140)
+ERROR HY000: Can't create table 'test.t1' (errno: 140)
 show warnings;
 Level	Code	Message
 Error	1296	Got error 739 'Unsupported primary key length' from NDB
-Error	1005	Can't create table './test/t1.frm' (errno: 140)
+Error	1005	Can't create table 'test.t1' (errno: 140)
 create table t1 (
 pk1 int not null primary key,
 b bit(9),
 key(b)
 ) engine=ndbcluster;
-ERROR HY000: Can't create table './test/t1.frm' (errno: 140)
+ERROR HY000: Can't create table 'test.t1' (errno: 140)
 show warnings;
 Level	Code	Message
 Error	1296	Got error 743 'Unsupported character set in table or index' from NDB
-Error	1005	Can't create table './test/t1.frm' (errno: 140)
+Error	1005	Can't create table 'test.t1' (errno: 140)