improve Spyc dependency loading

Spyc is a common dependency. To avoid double class loading, inject a
“class_exists” check around the Spyc class definition. It’s not
bullet-proof but should help in some situations at least.

fixes #832
issue #811
fixes #542

bin/fix_spyc_loading.php

@@ -0,0 +1,16 @@
+<?php
+$spyc_class_file = "vendor/mustangostang/spyc/Spyc.php";
+
+$handle = fopen($spyc_class_file, "r+");
+$content = fread($handle, filesize($spyc_class_file));
+
+// if the check has not already been added only
+if (!stripos($content, "if (!class_exists('Spyc'))")) {
+	$content = str_replace("class Spyc", "if (!class_exists('Spyc')) {\nclass Spyc", $content);
+	$content .= "\n}\n";
+
+	rewind($handle);
+	fwrite($handle, $content);
+}
+
+fclose($handle);

composer.json

@@ -23,5 +23,9 @@
         "pear/pear_exception": "1.0.*@dev",
         "podlove/comment-introspection": "dev-master",
         "phpunit/phpunit": "4.7.*"
+    },
+    "scripts": {
+        "post-update-cmd": [ "php bin/fix_spyc_loading.php" ],
+        "post-install-cmd": [ "php bin/fix_spyc_loading.php" ]
     }
 }