Safari automatically appends .txt extension to .ino files
It seems that this is a server issue. And one can't solve the issue by changing safari settings. The answers to the same question I found are in the below.

iMeowbot user in macrumors says that:


  "This filename modification stuff isn't something that Apple made up,
  it comes straight out of RFC 2183 (see "2.3 The Filename Parameter"
  and "5. Security Considerations"). While that RFC talks about
  "messages" and "mail" it applies equally to the Web, as HTTP employs
  MIME.
  
  OS X and Safari have no way to read the mind of the server operator,
  and cannot tell if a mismatched media type and filename are accidental
  or intentional. So, they follow the standard.
  
  Recent Safari versions add additional checks, such as that annoying
  prompt for when something appears to contain an executable file. It's
  all part of the same healthy paranoia that helps ensure that the end
  user knows exactly what a remote server is attempting to send."


http://forums.macrumors.com/threads/safari-adding-txt-to-a-m4v-download.167086/

TETENAL user in macnn says that:


  "AFAIK the Apache server software comes with a preset of
  extension->MIME-type assignments. If a file with an unknown extension
  (like .dmg) is served with the MIME-type text as a fallback, Safari
  adds a .txt extension. This behavior is arguably correct. The server
  tells Safari it is serving a text-file, and a text file needs a .txt
  extension on Mac to be opened with a text editor. So Safari adds one.
  Other browsers ignore the server, which is a short term benefit for
  the user, but in the long run a) makes the server admin not notice the
  mistake and b) prevents the server admin to use this feature whenever
  he intentionally wants to (as opposed to unintentionally doesn't care
  as usually).
  
  Anyway, to fix this you can create a file .htaccess to the respective
  folder and correctly define the missing MIME-types by adding AddType
  application/octet-stream .dmg or AddType application/x-stuffit .sit
  and AddType application/x-stuffit .sitx etc."


http://forums.macnn.com/82/applications/339922/safari-apending-txt-file-extensions-how/