emulators/dosbox: enable mouse locking with X.org newer than 1.20

References: https://www.vogons.org/viewtopic.php?f=31&t=62703

PR:     244960
Submitted by:   tobias.rehbein@web.de
Reviewed by:    knyght@gmail.com (maintainer)

emulators/dosbox/Makefile

@@ -3,6 +3,7 @@
 
 PORTNAME=	dosbox
 DISTVERSION=	0.74-3
+PORTREVISION=	1
 CATEGORIES=	emulators
 MASTER_SITES=	SF/${PORTNAME}/${PORTNAME}/${DISTVERSION}
 

emulators/dosbox/files/patch-src_gui_sdlmain.cpp

@@ -0,0 +1,11 @@
+--- src/gui/sdlmain.cpp.orig	2020-03-21 19:17:13 UTC
++++ src/gui/sdlmain.cpp
+@@ -1433,7 +1433,7 @@ void GFX_LosingFocus(void) {
+ #define DB_POLLSKIP 1
+ #endif
+ 
+-#if defined(LINUX)
++#if defined(LINUX) || defined(BSD)
+ #define SDL_XORG_FIX 1
+ #else
+ #define SDL_XORG_FIX 0