Creates the specified directory.
This function will only create the final directory in the path,
all intermediate directories must already exist.
Parameter:
dirspec
The directory to be created.
The directory name does not support wildcard characters.
On Unix-like systems, if the first character is a ~ (tilde)
character optionally followed by a username, it is replaced by the
current or specified user's home directory.
mode (Unix-like systems only)
The file permission bits of the new directory as a decimal
number between 0 (octal 000) and 511 (octal 777).
If not specified, mode defaults to 511
(octal 777).
Any mode restrictions specified by umask
will always be taken into account.
