build system update

From: David Abrahams (david.abrahams_at_[hidden])
Date: 2001-10-31 14:23:42

I have checked in a first cut at using command-files to overcome the
line-length limitation on NT, along with a couple of unrelated bug fixes. I
reduced MAXLINE back to 2047 so that it complies with experimental results.
To take advantage of this stuff you need to build jam from sources on the
jam_src branch in tools/build/jam_src and define the COMMAND_FILES variable.
Note that the command-file functionality is currently hard-coded into
msvc-tools.jam, but it needs to be factored out and used on a platform +
toolset-specific basis. There is still a mystery about why I had to write:

        DEPENDS $(<[1]) : $(command-file) ;
        RmTemps $(<[1]) : $(command-file) ;

as opposed to:

        DEPENDS $(<) : $(command-file) ;
        RmTemps $(<) : $(command-file) ;

In the link action; it was causing unneccessary DLL rebuilds otherwise. I'm
going to track that down in the debugger.

===================================================
  David Abrahams, C++ library designer for hire
 resume: http://users.rcn.com/abrahams/resume.html

        C++ Booster (http://www.boost.org)
          email: david.abrahams_at_[hidden]
===================================================