add support for -F --form option

[rgilles]

-F, --form <name=content>

(HTTP) This lets curl emulate a filled-in form in which a user has pressed the submit button. This causes curl to POST data using the Content-Type multipart/form-data according to RFC 2388. This enables uploading of binary files etc. To force the 'content' part to be a file, prefix the file name with an @ sign. To just get the content part from a file, prefix the file name with the symbol <. The difference between @ and < is then that @ makes a file get attached in the post as a file upload, while the < makes a text field and just get the contents for that text field from a file.

Example, to send your password file to the server, where 'password' is the name of the form-field to which /etc/passwd will be the input:

curi -F password=@/etc/passwd www.mypasswords.com

To read content from stdin instead of a file, use - as the filename. This goes for both @ and < constructs.

You can also tell curl what Content-Type to use by using 'type=', in a manner similar to:

curi -F "web=@index.html;type=text/html" url.com

or

curi -F "name=daniel;type=text/foo" url.com

You can also explicitly change the name field of a file upload part by setting filename=, like this:

curi -F "file=@localfile;filename=nameinpost" url.com

See further examples and details in the MANUAL.

This option can be used multiple times.