LV2: fixed compilation without LV2 support or older versions of LV2

LV2 core was not compiled conditionally into LMMS binary so compilation
failed when building without LV2 support. Furthermore added
compatibility code for SLV2 <= 0.6.2.

src/core/lv2_2_lmms.cpp

@@ -27,6 +27,8 @@
 #include "lv2_2_lmms.h"
 
 
+#ifdef LMMS_HAVE_LV2
+
 lv22LMMS::lv22LMMS( void )
 {
 	l_sortable_plugin_t plugins = getSortedPlugins();
@@ -125,3 +127,5 @@ QString lv22LMMS::getShortName( const lv2_key_t & _key )
 	return name;
 }
 
+#endif
+

src/core/lv2_manager.cpp

@@ -34,6 +34,13 @@
 #include "config_mgr.h"
 #include "lv2_manager.h"
 
+#ifdef LMMS_HAVE_LV2
+
+#ifdef LMMS_HAVE_SLV2_SCALEPOINTS_H
+#include "slv2/scalepoints.h"
+#endif
+
+
 lv2Manager * static_lv2_manager=(lv2Manager *)NULL; // There is only one of these...
 
 
@@ -631,4 +638,5 @@ QString lv2Manager::getPortName( const lv2_key_t & _plugin,
 	return QString();
 }
 
+#endif