Revert "Use print_form_button() instead of print_small_button()"

Trying to detach an Issue from a Changeset always results in
APPLICATION ERROR 2800 - Invalid form security token, even when using
a valid token.

This is because print_form_button() currently does not work with action
URLs generated by plugin_page(), see [1].

So we revert to original behavior of using print_small_button() (as it
was before commit 787eaa8), but keeping
the single form security token implemented in commit
634277d.

This change can be reverted again, once the upstream issue has been
fixed.

Issue #372

[1]: https://mantisbt.org/bugs/view.php?id=28533

Source/pages/view.php

@@ -185,7 +185,7 @@ function( $p_bug_id ) use ( $t_view_bug_threshold ) {
 <?php
 $t_first = true;
 $t_user_id = auth_get_current_user_id();
-$t_security_token = form_security_token( 'plugin_Source_detach' );
+$t_security_token = form_security_param( 'plugin_Source_detach' );
 
 foreach ( $t_bug_rows as $t_bug_id => $t_bug_row ) {
 	$t_color_class = html_get_status_css_fg(
@@ -213,12 +213,11 @@ function( $p_bug_id ) use ( $t_view_bug_threshold ) {
 </td>
 <?php if ( $t_can_update ) { ?>
 <td class="center"><?php
-	print_form_button(
-		plugin_page( 'detach' ),
-		plugin_lang_get( 'detach' ),
-		array( 'id' => $t_changeset->id, 'bug_id' => $t_bug_id),
-		$t_security_token,
-		'btn btn-round btn-white btn-primary btn-sm'
+	$t_param = array( 'id' => $t_changeset->id, 'bug_id' => $t_bug_id);
+	print_small_button(
+		plugin_page( 'detach' )
+		. '&' . http_build_query( $t_param ) . $t_security_token,
+		plugin_lang_get( 'detach' )
 	) ?>
 </td>
 <?php } ?>