Build system update

From: David Abrahams (abrahams_at_[hidden])
Date: 2001-06-07 22:48:42

In CVS:
--------

Added subproject and subinclude rules, now using them in Jamfiles.

Changed TOOLSET_DIR to BOOST_TOOLSET_DIR

features.jam is now located in $(BOOST_TOOLSET_DIR), if supplied.

borland-tools.jam now has a new system for finding the tools, which puts less
pressure on users to have everything in their PATH. All toolset descriptions
will use this system. Also fixed conflicting tool definitions.

Added documentation on installing Jam and initiating a build. Also documented
the neccessary Jam support files. Documented the Jamrules file. Added a simple
example Jamfile.

Removed flotsam uses of CCFLAGS and OPTIM variables from toolset description
files.

Fixed metrowerks support to actually respond to CFLAGS features!