Fix/improve includes/fwd decls

Preparation for clang-format. It will shuffle the includes, and this
preparation will prevent errors from that step.

plugins/MidiImport/portsmf/algrd_internal.h

@@ -1,5 +1,7 @@
 /* algread_internal.h -- interface between allegro.cpp and allegrord.cpp */
 
+#include "allegro.h"
+
 Alg_error alg_read(std::istream &file, Alg_seq_ptr new_seq, 
                    double *offset_ptr = NULL);
 

plugins/MidiImport/portsmf/algsmfrd_internal.h

@@ -1,3 +1,5 @@
 /* algsmfrd_internal.h -- interface from allegrosmfrd.cpp to allegro.cpp */
 
+#include "allegro.h"
+
 Alg_error alg_smf_read(std::istream &file, Alg_seq_ptr new_seq);

plugins/MidiImport/portsmf/allegro.h

@@ -49,6 +49,7 @@
 #ifndef ALLEGRO_H
 #define ALLEGRO_H
 #include <assert.h>
+#include <cstring>
 #include <istream>
 #include <ostream>
 

plugins/MidiImport/portsmf/mfmidi.h

@@ -1,3 +1,5 @@
+#include <cstddef>
+
 #define NOTEOFF 0x80
 #define NOTEON 0x90
 #define PRESSURE 0xa0

plugins/peak_controller_effect/peak_controller_effect.h

@@ -29,6 +29,8 @@
 #include "Effect.h"
 #include "peak_controller_effect_controls.h"
 
+class PeakController;
+
 class PeakControllerEffect : public Effect
 {
 public:

plugins/zynaddsubfx/RemoteZynAddSubFx.cpp

@@ -29,7 +29,11 @@
 
 #include <queue>
 
+#include <FL/x.H>
+#undef CursorShape // is, by mistake, not undefed in FL
+
 #define BUILD_REMOTE_PLUGIN_CLIENT
+
 #include "Note.h"
 #include "RemotePlugin.h"
 #include "RemoteZynAddSubFx.h"
@@ -38,8 +42,6 @@
 #include "zynaddsubfx/src/Nio/Nio.h"
 #include "zynaddsubfx/src/UI/MasterUI.h"
 
-#include <FL/x.H>
-
 
 class RemoteZynAddSubFx : public RemotePluginClient, public LocalZynAddSubFx
 {