replace env variable injection with pervasive expando support

do not inject SOURCEDIR and BUILDDIR into the environment of
build steps and run configurations any more.
instead, all custom executable paths, argument lists and working
directories now support the %{sourceDir} and %{buildDir} macros.
this approach is more elegant and more scalable.

src/plugins/qt4projectmanager/qt4buildconfiguration.cpp

@@ -213,10 +213,6 @@ Utils::Environment Qt4BuildConfiguration::baseEnvironment() const
     Utils::Environment env = BuildConfiguration::baseEnvironment();
     qtVersion()->addToEnvironment(env);
 
-    // We can't call buildDirectory() since that uses environment() to expand,
-    // thus calling baseEnvironment() again
-    env.set(QLatin1String("BUILDDIR"), QDir::toNativeSeparators(env.expandVariables(rawBuildDirectory())));
-
     ToolChain *tc = toolChain();
     if (tc)
         tc->addToEnvironment(env);