Other: change how pkg-config includes are handeles

Wrote some own functions to hande pkg-config includes.
now Makefile generation will stop if xmms2-client-cpp.pc is missing
Now, compilation should work, even if xmms2-client-cpp development files
where installed after qmake das called for the first time.
also enabled adding files in the playlistview contextmenu

src/playlist/playlistview.cpp

@@ -188,7 +188,8 @@ PlaylistView::contextMenuEvent (QContextMenuEvent *e)
 
 	a = new QAction (tr ("Add file"), this);
 	a->setShortcut (tr ("Ctrl+F"));
-	a->setEnabled(false); // FIXME: Disabled for now
+	connect (a, SIGNAL (triggered ()),
+	         qobject_cast<PlaylistWidget *> (parent ()), SLOT (menuAddFile ()));
 	qm.addAction (a);
 
 	a = new QAction (tr ("Remove selected"), this);

src/src.pro

@@ -1,6 +1,7 @@
 TEMPLATE = app
 
 include (../config.pri)
+load (../features/pkgconfig.prf)
 
 COMPONENTS+=../lib/liblib.a
 LIBS += $$COMPONENTS
@@ -28,7 +29,13 @@ QMAKE_CXXFLAGS += -g
 ;CONFIG += debug warn_on
 QMAKE_CXXFLAGS_WARN_ON += -Wno-unused-parameter
 
-CONFIG += link_pkgconfig
-PKGCONFIG += xmms2-client-cpp xmms2-client
+XMMSCLIENTPKG += xmms2-client-cpp
+pkgconfig_exists ($$XMMSCLIENTPKG) {
+	QMAKE_CXXFLAGS  += $$pkgconfig_cflags($$XMMSCLIENTPKG)
+	LIBS += $$pkgconfig_libs($$XMMSCLIENTPKG)
+} else {
+	error (Please install the xmms2 c++ client library)
+}
+
 ;CONFIG += avahi