more windows Makefile tinkering

It looks like the Windows API call for PlaySound using SND_RESOURCE, from a
mingw32 built program, cannot find the resources that are
embeded into the .exe by the mingw32 resource compiler. That works fine
from visual studio.

For now, fall back to not using the SND_RESOURCE flag, use an ordinary
wav file name in the filesystem. Makefile.mingw32 has been modified
to copy the wav files to the binary directory along with the exe.

This probably won't be the final approach, but it will get things
working for now.

sys/windows/windmain.c

@@ -1056,10 +1056,12 @@ void freefakeconsole(void)
 }
 #endif
 
+static boolean path_buffer_set = FALSE;
+static char path_buffer[MAX_PATH];
+
 char *
 get_executable_path(void)
 {
-    static char path_buffer[MAX_PATH];
 
 #ifdef UNICODE
     {
@@ -1077,9 +1079,22 @@ get_executable_path(void)
     if (seperator)
         *seperator = '\0';
 
+    path_buffer_set = TRUE;
     return path_buffer;
 }
 
+#ifdef __MINGW32__
+char *
+exepath(void)
+{
+    char *p = (char *) 0;
+
+    if (path_buffer_set)
+        p = path_buffer;
+    return p;
+}
+#endif
+
 char *
 translate_path_variables(const char* str, char* buf)
 {