The master class is the template for the top level package. The only
build function performed by such a directory is the creation of the
system Tcl index file in $AST_ETC/tclIndex. This is done after
building all the sub-directories which are all modules at this level.
The master class obeys the EXPORT and EXPORT_SOURCE targets
which construct binary+source and source only releases respectively. The
release is written to a compressed tar file, the location of which
is specified using the EXPORT environment variable, the default
being the current directory.