/*
 * call-seq:
 *   Curl::PostField.content(name, content) => #<Curl::PostField...>
 *   Curl::PostField.content(name, content, content_type = nil) => #<Curl::PostField...>
 *   Curl::PostField.content(name, content_type = nil) { |field| ... } => #<Curl::PostField...>
 * 
 * Create a new Curl::PostField, supplying the field name, content,
 * and, optionally, Content-type (curl will attempt to determine this if
 * not specified).
 * 
 * The block form allows a block to supply the content for this field, called
 * during the perform. The block should return a ruby string with the field
 * data.
 */
static VALUE ruby_curl_postfield_new_content(int argc, VALUE *argv, VALUE klass) {