After squashing most of our compiler warnings, up'ed the default
warning level from 3 to 4 in order to increase the likelyhood of
catching future warnings.
Updated the makefiles and Visual Studio project files to support moving
the authentication code to the new lib/vauth directory that was started
in commit 0d04e859e1.
In preparation for adding the test suite and examples projects renamed
the top level "all" solution files to better describe what they are.
This will also enable us to use "curl" rather than "curlsrc" for the
command line tool solution and project files, which will simplify some
of the configuration.
Defined the DEBUGBUILD pre-processor variable to allow extra logging,
which is particularly useful in debug builds, as we use this and Visual
Studio typically uses _DEBUG.
We could define DEBUBBUILD, in curl_setup.h, when _MSC_VER and _DEBUG is
defined but that would also affect the makefile based builds which we
probably don't want to do.
Carrying on from commit 11025613b9 added a more thorough version of
the VC6 project files which are capable of supporting side-by-side
compilation, as well as support for some of the third-party libraries
curl uses.
