Remove "iconv" PHP extension dependency

Summary: Depends on D20069. Ref T13232. This is a very, very weak dependency and we can reasonably polyfill it.

Test Plan: Grepped for `iconv` in libphutil, arcanist, and Phabricator.

Reviewers: amckinley

Reviewed By: amckinley

Maniphest Tasks: T13232

Differential Revision: https://secure.phabricator.com/D20070

Author: epriestley

scripts/mail/mail_handler.php

@@ -55,8 +55,8 @@
 }
 
 $headers = $parser->getHeaders();
-$headers['subject'] = iconv_mime_decode($headers['subject'], 0, 'UTF-8');
-$headers['from'] = iconv_mime_decode($headers['from'], 0, 'UTF-8');
+$headers['subject'] = phutil_decode_mime_header($headers['subject']);
+$headers['from'] = phutil_decode_mime_header($headers['from']);
 
 if ($args->getArg('process-duplicates')) {
   $headers['message-id'] = Filesystem::readRandomCharacters(64);

src/applications/config/check/PhabricatorExtensionsSetupCheck.php

@@ -11,14 +11,13 @@ public function isPreflightCheck() {
   }
 
   protected function executeChecks() {
-    // TODO: Make 'mbstring' and 'iconv' soft requirements.
+    // TODO: Make 'mbstring' a soft requirement.
 
     $required = array(
       'hash',
       'json',
       'openssl',
       'mbstring',
-      'iconv',
       'ctype',
 
       // There is a tiny chance we might not need this, but a significant

src/applications/config/controller/PhabricatorConfigVersionController.php

@@ -63,6 +63,8 @@ public function renderModuleStatus($viewer) {
         $version_from_file);
     }
 
+    $version_property_list->addProperty('php', phpversion());
+
     $binaries = PhutilBinaryAnalyzer::getAllBinaries();
     foreach ($binaries as $binary) {
       if (!$binary->isBinaryAvailable()) {