lynx-dev Fixing the display corruption bug for pdcurses/slang lynx.exe

[vtailor]

The code causing the display corruption is in XSystem.c.  The following
fix restores the display properly after calling a viewer in both pdcurses
and slang lynx.exe:

#ifdef __MINGW32__
int exec_command(char * cmd, int wait_flag)
{
        return system(cmd);
}
#else
int exec_command(char * cmd, int wait_flag)
{
    PRO *p;
    char *pif;
    int rc = 0;
    int cmd_str;
        ...
}
#endif