added new function test_if_data_home_dir() which checks that
path does not contain mysql data home directory.
Using of 'mysql data home'/'any db name' in
DATA DIRECTORY & INDEX DIRECTORY is disallowed
- The function build_table_filename() builds up a string unconditionally
using the forward slash as a path separator. Later, when the string is
searched for FN_LIBCHAR by the set_up_table_before_create() function, a
null pointer is returned that is finally used by strlen in the
append_file_to_dir() function which causes the crash.
