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/gui/scan.cpp

@@ -2,7 +2,7 @@
 	Neutrino-GUI  -   DBoxII-Project
 
 	Copyright (C) 2001 Steffen Hehn 'McClean'
-	Copyright (C) 2011-2012 Stefan Seyfried
+	Copyright (C) 2011-2013,2015,2017 Stefan Seyfried
 
 	License: GPL
 
@@ -169,6 +169,13 @@ int CScanTs::exec(CMenuTarget* /*parent*/, const std::string & actionKey)
 	bool test = actionKey == "test";
 	bool manual = (actionKey == "manual") || test;
 	bool fast = (actionKey == "fast");
+#if !ENABLE_FASTSCAN
+	if (fast) {
+		/* popup message? But this *should* be impossible to happen anyway */
+		fprintf(stderr, "CScanTs::exec: fastscan disabled at build-time!\n");
+		return menu_return::RETURN_REPAINT;
+	}
+#endif
 
 	if (CFrontend::isSat(delsys))
 		pname = scansettings.satName;
@@ -299,8 +306,10 @@ int CScanTs::exec(CMenuTarget* /*parent*/, const std::string & actionKey)
 	} else if(manual)
 		success = g_Zapit->scan_TP(TP);
 	else if(fast) {
+#if ENABLE_FASTSCAN
 		CServiceScan::getInstance()->QuietFastScan(false);
 		success = CZapit::getInstance()->StartFastScan(scansettings.fast_type, scansettings.fast_op);
+#endif
 	}
 	else
 		success = g_Zapit->startScan(scan_flags);