Fix preprocessor logic

The C++ preprocessor is actually not required to process "true" and "false"
correctly. This works in C if <stdbool.h> is included, because these are
then macros themselves, and resolved correctly, but C++ requires them to be
keywords, so no such macros exist, and the preprocessor can treat both as
undefined/zero.

pcbnew/files.cpp

@@ -56,8 +56,8 @@
 #include <wx/stdpaths.h>
 
 
-//#define     USE_INSTRUMENTATION     true
-#define     USE_INSTRUMENTATION     false
+//#define     USE_INSTRUMENTATION     1
+#define     USE_INSTRUMENTATION     0
 
 
 static const wxChar backupSuffix[]   = wxT( "-bak" );