trx_sys_file_format_max_upgrade(): Rename from
trx_sys_file_format_max_update().  Improve the documentation.  Add a
const qualifier to the parameter "name".  Replace the parameter
"flags" with "format_id", because this function should deal with file
format identifiers, not with table flags.

trx_sys_file_format_max_write(), trx_sys_file_format_max_set(): Add a
const qualifier to the parameter "name".

ha_innodb.cc: Correct the spelling in some comments: "side effect".
Remove redundant prototypes for some static callback functions.

innodb_file_format_name_update(), innodb_file_format_check_update():
Correct the function signature.  Use appropriate pointer type conversions.

MYSQL_SYSVAR_STR(file_format), MYSQL_SYSVAR_STR(file_format_check):
Remove the type conversions from the callback function pointers.  When
the function signatures match, no type conversion is needed.  The type
conversions would only prevent compilation warnings for any mismatch.

Approved by Sunny in rb://25.