Fix compilation warning by giving boot function a proper return type

Author: Leont

Changes

@@ -1,6 +1,7 @@
 Revision history for File-Map
 
 {{$NEXT}}
+          Fix compilation warning by giving boot function a proper return type
 
 0.64      2015-07-13 12:50:12+02:00 Europe/Amsterdam
           Fix segfault in empty mappings

lib/File/Map.xs

@@ -436,7 +436,7 @@ static int S_protection_value(pTHX_ SV* mode, int fallback) {
 		XSRETURN_EMPTY;\
 	} STMT_END
 
-static boot(pTHX) {
+static void boot(pTHX) {
 	AV* constants = newAV();
 	HV* stash = get_hv("File::Map::", FALSE);
 	HV* advise_constants = newHV();