add --enable-fastscan configure option

The #define in src/gui/scan_setup.h did not work (undefining
ENABLE_FASTSCAN caused really strange side effects wrt background
scanning in standby mode), and all the unused code was still built.
With this configure option, people who really want this obscure feature
can enable it for their builds.


Origin commit data
------------------
Branch: ni/coolstream
Commit: 6525d1164a
Author: Stefan Seyfried <seife@tuxbox-git.slipkontur.de>
Date: 2017-02-04 (Sat, 04 Feb 2017)



------------------
This commit was generated by Migit

src/neutrino.cpp

@@ -4,7 +4,7 @@
 	Copyright (C) 2001 Steffen Hehn 'McClean'
 							 and some other guys
 
-	Copyright (C) 2006-2016 Stefan Seyfried
+	Copyright (C) 2006-2017 Stefan Seyfried
 
 	Copyright (C) 2011 CoolStream International Ltd
 
@@ -4852,6 +4852,7 @@ void CNeutrinoApp::Cleanup()
 #endif
 }
 
+#if ENABLE_FASTSCAN
 void CNeutrinoApp::CheckFastScan(bool standby, bool reload)
 {
 	if (scansettings.fst_update) {
@@ -4883,6 +4884,11 @@ void CNeutrinoApp::CheckFastScan(bool standby, bool reload)
 		}
 	}
 }
+#else
+void CNeutrinoApp::CheckFastScan(bool, bool)
+{
+}
+#endif
 
 bool CNeutrinoApp::adjustToChannelID(const t_channel_id channel_id)
 {