Reviewed by Ariya Hidayat.

If no configuration is specified when building WebKit we pass the
debug_and_release option to QMake which results in Makefiles for
both configurations being generated.

Previously we built both of these configurations by default, for
all targets (both the QtWebKit framework/dyldlib and the various
executables such as QtLauncher and tests). This makes sense for
the libraries, which get the _debug suffix and can be loaded on
demand by setting the DYLD_IMAGE_SUFFIX, but for executables we
ended up building the same executable twice.

We now only build one instance of each executable, and since this
is a developer build we build the debug-version. Passing either
--debug or --release to build-webkit will override this, and
even in the default case the release version can still be built
by running 'make release' in the the build directory of each
target.

* WebCore.pro:
* DumpRenderTree/qt/TestNetscapePlugin/TestNetscapePlugin.pro:
* Scripts/webkitdirs.pm:

git-svn-id: http://svn.webkit.org/repository/webkit/trunk@47743 268f45cc-cd09-0410-ab3c-d52691b4dbfc