Add substitutions %t, %j, and %J as path-safe variants of %T, %i, and %I.

Add substitutions %t, %j, and %J as path-safe variants of %T, %i, and %I.

Rationale: Using the existing substitutions in construction of paths
(dynamic shares, created on client connect) results in directory names with
colons and dots in them. Those can be hard to use when accessed from a
different share, as Windows does not allow : in paths and has some ideas about
dots.

Signed-off-by: Dr. Thomas Orgis <thomas.orgis@uni-hamburg.de>
Reviewed-by: Andrew Bartlett <abartlet@samba.org>
Reviewed-by: Garming Sam <garming@catalyst.net.nz>