Move SystemDirsAppend to own header

This function is called only from three sites, it doesn't need to be in
common.h.

The implementation was already in systemdirsappend.cpp, so a matching
header was created for it.

This reduces the visibility of the function to only the files that need
it and slightly shrinks common.h.

common/kiface_i.cpp

@@ -29,6 +29,7 @@
 
 #include <kiface_i.h>
 #include <pgm_base.h>
+#include <systemdirsappend.h>
 
 #include <common.h>
 

common/pgm_base.cpp

@@ -52,6 +52,7 @@
 #include <confirm.h>
 #include <dialog_env_var_config.h>
 #include <lockfile.h>
+#include <systemdirsappend.h>
 
 
 #define KICAD_COMMON                     wxT( "kicad_common" )

include/common.h

@@ -304,16 +304,6 @@ double RoundTo0( double x, double precision );
  */
 void wxStringSplit( const wxString& aText, wxArrayString& aStrings, wxChar aSplitter );
 
-
-/**
- * Function SystemDirsAppend
- * appends system places to aSearchStack in a platform specific way, and pertinent
- * to KiCad programs.  It seems to be a place to collect bad ideas and keep them
- * out of view.
- */
-void SystemDirsAppend( SEARCH_STACK* aSearchStack );
-
-
 /**
  * Function SearchHelpFileFullPath
  * returns the help file's full path.

include/systemdirsappend.h

@@ -0,0 +1,42 @@
+/*
+ * This program source code file is part of KiCad, a free EDA CAD application.
+ *
+ * Copyright (C) 2017 KiCad Developers, see AUTHORS.txt for contributors.
+ *
+ * This program is free software; you can redistribute it and/or
+ * modify it under the terms of the GNU General Public License
+ * as published by the Free Software Foundation; either version 2
+ * of the License, or (at your option) any later version.
+ *
+ * This program is distributed in the hope that it will be useful,
+ * but WITHOUT ANY WARRANTY; without even the implied warranty of
+ * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
+ * GNU General Public License for more details.
+ *
+ * You should have received a copy of the GNU General Public License
+ * along with this program; if not, you may find one here:
+ * http://www.gnu.org/licenses/old-licenses/gpl-2.0.html
+ * or you may search the http://www.gnu.org website for the version 2 license,
+ * or you may write to the Free Software Foundation, Inc.,
+ * 51 Franklin Street, Fifth Floor, Boston, MA  02110-1301, USA
+ */
+
+/**
+ * System directories search utilities
+ * @file systemdirsappend.h
+ */
+
+#ifndef INCLUDE__SYSTEM_DIRS_APPEND_H_
+#define INCLUDE__SYSTEM_DIRS_APPEND_H_
+
+class SEARCH_STACK;
+
+/**
+ * Function SystemDirsAppend
+ * appends system places to aSearchStack in a platform specific way, and pertinent
+ * to KiCad programs.  It seems to be a place to collect bad ideas and keep them
+ * out of view.
+ */
+void SystemDirsAppend( SEARCH_STACK* aSearchStack );
+
+#endif  // INCLUDE__SYSTEM_DIRS_APPEND_H_

kicad/kicad.cpp

@@ -38,6 +38,8 @@
 #include <kiway.h>
 #include <richio.h>
 #include <wildcards_and_files_ext.h>
+#include <systemdirsappend.h>
+
 #include <stdexcept>
 
 #include "pgm_kicad.h"