Fix build against libmemcached versions before 0.39.

memcached_server_instance_st was defined in 0.39. Built and tested
against 0.31 and 0.49.

Author: tricky

package.xml

@@ -64,6 +64,7 @@ http://pear.php.net/dtd/package-2.0.xsd">
    <file role='src' name='php_memcached.h'/>
    <file role='src' name='php_memcached_session.c'/>
    <file role='src' name='php_memcached_session.h'/>
+   <file role='src' name='php_libmemcached_compat.h'/>
    <file role='src' name='g_fmt.c'/>
    <file role='src' name='g_fmt.h'/>
    <file role='src' name='fastlz/fastlz.c'/>

php_libmemcached_compat.h

@@ -0,0 +1,16 @@
+/*
+ * Here we define backwards compatibility for older
+ * libmemcached API:s
+ *
+ *      // Teddy Grenman <[email protected]>
+ */
+
+#ifndef PHP_LIBMEMCACHED_COMPAT
+#define PHP_LIBMEMCACHED_COMPAT
+
+#if !defined(LIBMEMCACHED_VERSION_HEX) || LIBMEMCACHED_VERSION_HEX < 0x00039000
+/* definition from libmemcached/types.h version 0.39+ */
+typedef const struct memcached_server_st *memcached_server_instance_st;
+#endif
+
+#endif

php_memcached.c

@@ -45,6 +45,7 @@
 #include <ext/standard/basic_functions.h>
 #include <libmemcached/memcached.h>
 
+#include "php_libmemcached_compat.h"
 #include "php_memcached.h"
 #include "g_fmt.h"
 

php_memcached_session.c

@@ -47,7 +47,7 @@ ps_module ps_mod_memcached = {
 /*
  * Stolen from libmemcached/common.h, because we need it and they don't expose it.
  */
-static inline memcached_return_t memcached_validate_key_length(size_t key_length, bool binary)
+static inline int memcached_validate_key_length(size_t key_length, bool binary)
 {
 	if (key_length == 0)
 		return MEMCACHED_BAD_KEY_PROVIDED;