Description: When 'mysql_real_connect()' is invoked in
parallel with either of the option MYSQL_READ_DEFAULT_FILE
or MYSQL_READ_DEFAULT_GROUP enabled causes a noticeable
percentage of thread connection failures. This is due to the
inappropriate loading of options from the configuration
files.

Analysis: 'mysql_real_connect()' calls 'my_load_defaults()'
which will toggle a static global variable 'is_login_file'
before it calls 'my_search_option_files()'. Function
'my_search_option_files()'  has conditional logic based on
the static global variable, 'is_login_file', which is
accessible across multiple threads. This makes
'mysql_real_connect()' thread unsafe causing noticeable
percent of parallel thread connections to fail.

Fix: A new argument, 'is_login_file', is passed to all the
functions which deals with login file.