Add missing source files to package.xml

Author: kleisauke

package.xml

@@ -41,6 +41,8 @@ http://pear.php.net/dtd/package-2.0.xsd">
    <file role='src' name='config.w32'/>
    <file role='src' name='php_vips.h'/>
    <file role='src' name='vips.c'/>
+   <file role='src' name='vips.stub.php'/>
+   <file role='src' name='vips_arginfo.h'/>
 
    <dir name="tests">
     <file role='test' name='001.phpt'/>