[PHP] Add support for PHP7.

PHP5's C extension API has changed substantially so you need to use
-php7 to specify you want PHP7 compatible wrappers.
Fixes https://github.com/swig/swig/issues/571

Examples/php5/pragmas/example.i

@@ -0,0 +1,31 @@
+/* File : example.i */
+%module example
+
+%init{
+  zend_printf("This was %%init\n");
+}
+
+%minit{
+  zend_printf("This was %%minit\n");
+}
+
+%mshutdown{
+  zend_printf("This was %%shutdown\n");
+}
+
+%rinit{
+  zend_printf("This was %%rinit\n");
+}
+
+%rshutdown{
+  zend_printf("This was %%rshutdown\n");
+}
+
+%pragma(php) include="include.php";
+
+%pragma(php) code="
+# This code is inserted into example.php
+echo \"this was php code\\n\";
+"
+
+%pragma(php) phpinfo="php_info_print_table_start();"