gcc initialization revised

From: Vladimir Prus (ghost_at_[hidden])
Date: 2004-06-11 05:56:59

I've just changed the gcc initialization according the the approach we've 
discussed recently.

Now, things like:

using gcc ;
using gcc ;

produce the following:

error: duplicate initialization of gcc with the following parameters:
error: version = <unspecified>
error: at /home/ghost/user-config.jam:13

And thing like:

using gcc ;
using gcc : 3.4 g++3.4 ;

produce this:

error: gcc initialization: parameter 'version' inconsistent
error: no value was specified in earlier initialization
error: an explicit value is specified now
error: at /home/ghost/user-config.jam:13

The most important new change is that "version" parameter should either be 
specified in all calls to "using", or not specified in any call.

If the are no problems which this change, I'll look at applyting the same rule 
to other toolsets.

Ah, and there's unrelated but nice change: there's a new 'errors.user-error' 
rule which is almost like 'errors.error', but shows only user modules in the 
backtrace. That's why the above messages don't mention toolset.using, 
gcc.init and common.check-init-parameters ;-)

- Volodya