[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

Lib/php5/std_string.i

@@ -0,0 +1,79 @@
+/* -----------------------------------------------------------------------------
+ * std_string.i
+ *
+ * SWIG typemaps for std::string types
+ * ----------------------------------------------------------------------------- */
+
+// ------------------------------------------------------------------------
+// std::string is typemapped by value
+// This can prevent exporting methods which return a string
+// in order for the user to modify it.
+// However, I think I'll wait until someone asks for it...
+// ------------------------------------------------------------------------
+
+%include <exception.i>
+
+%{
+#include <string>
+%}
+
+namespace std {
+
+    %naturalvar string;
+
+    class string;
+
+    %typemap(typecheck,precedence=SWIG_TYPECHECK_STRING) string, const string& %{
+        $1 = ( Z_TYPE_PP($input) == IS_STRING ) ? 1 : 0;
+    %}
+
+    %typemap(in) string %{
+        convert_to_string_ex($input);
+        $1.assign(Z_STRVAL_PP($input), Z_STRLEN_PP($input));
+    %}
+
+    %typemap(directorout) string %{
+        convert_to_string_ex(&$input);
+        $result.assign(Z_STRVAL_P($input), Z_STRLEN_P($input));
+    %}
+
+    %typemap(out) string %{
+        ZVAL_STRINGL($result, const_cast<char*>($1.data()), $1.size(), 1);
+    %}
+
+    %typemap(directorin) string, const string& %{
+        ZVAL_STRINGL($input, const_cast<char*>($1.data()), $1.size(), 1);
+    %}
+
+    %typemap(out) const string & %{
+        ZVAL_STRINGL($result, const_cast<char*>($1->data()), $1->size(), 1);
+    %}
+
+    %typemap(throws) string, const string& %{
+        zend_throw_exception(NULL, const_cast<char*>($1.c_str()), 0 TSRMLS_CC);
+        return;
+    %}
+
+    /* These next two handle a function which takes a non-const reference to
+     * a std::string and modifies the string. */
+    %typemap(in) string & ($*1_ltype temp) %{
+        convert_to_string_ex($input);
+        temp.assign(Z_STRVAL_PP($input), Z_STRLEN_PP($input));
+        $1 = &temp;
+    %}
+
+    %typemap(directorout) string & ($*1_ltype *temp) %{
+        convert_to_string_ex(&$input);
+        temp = new $*1_ltype(Z_STRVAL_P($input), Z_STRLEN_P($input));
+        swig_acquire_ownership(temp);
+        $result = temp;
+    %}
+
+    %typemap(argout) string & %{
+	ZVAL_STRINGL(*($input), const_cast<char*>($1->data()), $1->size(), 1);
+    %}
+
+    /* SWIG will apply the non-const typemap above to const string& without
+     * this more specific typemap. */
+    %typemap(argout) const string & "";
+}