set default MS_MAP_BAD_PATTERN in Apache conf

[Jeff McKenna]

• since MapServer 7.6.3, MapServer prevents MAP= directory traversing, and sets a hardcoded MS_MAP_BAD_PATTERN
• for the next MS4W release, Apache's httpd.conf must also contain a new default bad pattern, that specifically works with MS4W (and its PCRE regex library) :

    SetEnv MS_MAP_BAD_PATTERN "[\/\\\\]{2}|[\/\\\\]?\.{2,}[\/\\\\]|,"
  

which allows /./ but not /../ or /.../

• otherwise a scary and tricky error message will be returned:

    msCGILoadMap(): Web application error. CGI variable "map" fails to validate. msEvalRegex(): Regular expression error. Failed to compile expression ([/\]{2}|[/\]?\.+[/\]|,). 
  

• This should also be documented in the readme (ticket#317)
• it should also be documented that this can be disabled with:

    SetEnv MS_MAP_BAD_PATTERN "false"
  

• This should also be set inside setenv.bat