Excluding directories
---------------------
An alias module may exclude particular directories from other
modules by using an exclamation mark (`!') before the name of each
directory to be excluded.
For example, if the modules file contains:
exmodule -a !first-dir/sdir first-dir
then checking out the module `exmodule' will check out everything in
`first-dir' except any files in the subdirectory `first-dir/sdir'.