proposal for make help chain-build text

[Patrice Dumas <pertusus free fr>]

Hello,

Here is a proposal for the result of make help for the chain-build
target, what I changed relates with : and prallel builds:

        chain-build             Build current package in order with
other packages
                example:  make chain-build CHAIN='libwidget libgizmo'
                The current package is added to the end of the CHAIN list.
                Colons (:) can be used in the CHAIN parameter to define 
                parallely built package groups.
                Packages in a single group will be built in parallel,
                and all packages in a group must build successfully and 
                populate the repository before the next group will begin building. 
                For example
                make chain-build CHAIN='libwidget libaselib : libgizmo
:'
                will cause libwidget and libaselib to be build in parallel, 
                followed by libgizmo and then the current directory package.
                If no groups are defined, packages will be built sequentially.


--
Pat