add .cmd support to generic-x.el

[tury . peter]

Hi,

--->8----
maybe this is not the right place for such demands. If this is the case please 
write me where should I send such requests. Thanks!
--->8----

My generic-x.el doesn't know MS Windows' .cmd extension. As far as I know this 
is the same as .bat files, so I added 
"\\.[cC][mM][dD]\\'"
to the file extension list of bat-generic-mode. It works now fine for me (as I 
usually create .cmd files).

Please do the same to the official version also!

Thanks,
P