Fixed Linux compilation error. Since dlopen() doesn't support RTLD_FIRST on...

Fixed Linux compilation error.  Since dlopen() doesn't support RTLD_FIRST on Linux, both plugin initializer functions are now mandatory.

olla/include/openmm/PluginInitializer.h

@@ -9,7 +9,7 @@
  * Biological Structures at Stanford, funded under the NIH Roadmap for        *
  * Medical Research, grant U54 GM072970. See https://simtk.org.               *
  *                                                                            *
- * Portions copyright (c) 2009 Stanford University and the Authors.           *
+ * Portions copyright (c) 2009-2011 Stanford University and the Authors.      *
  * Authors: Peter Eastman                                                     *
  * Contributors:                                                              *
  *                                                                            *
@@ -33,24 +33,23 @@
  * -------------------------------------------------------------------------- */
 
 /**
- * This file contains declarations for initialization functions that may be defined
+ * This file contains declarations for initialization functions that must be defined
  * by plugins, and that are invoked after the plugins have been loaded.  There are
  * two such functions: one for registering new Platforms, and one for adding new
- * KernelFactories to existing Platforms.  Each of these functions is optional; most
- * plugins implement one or the other of them, but not both.
+ * KernelFactories to existing Platforms.
  */
 
 /**
- * If a plugin defines a new Platform, it should define this function.  It will be
- * invoked after the plugin is loaded, and should register the new Platform by
+ * This function registers new Platforms that are defined by the plugin.  It will be
+ * invoked after the plugin is loaded, and should register the new Platforms by
  * calling Platform::registerPlatform().
  */
 extern "C" void registerPlatforms();
 
 /**
- * If a plugin defines a new KernelFactory for an existing Platform, it should define
- * this function.  It will be invoked after the plugin is loaded, and should register
- * the new factory by calling registerKernelFactory() on the appropriate Platform object.
+ * This function registers new KernelFactories for existing Platforms.
+ * It will be invoked after the plugin is loaded, and should register
+ * the new factories by calling registerKernelFactory() on the appropriate Platform objects.
  * It is not invoked until after registerPlatforms() has been called on every plugin,
  * thus avoiding initialization order problems when one plugin adds a KernelFactory
  * to a Platform defined by another plugin.

olla/src/Platform.cpp

@@ -182,7 +182,7 @@ static void initializePlugins(vector<HMODULE>& plugins) {
 }
 #else
 static void* loadOneLibrary(const string& file) {
-    void *handle = dlopen(file.c_str(), RTLD_LAZY | RTLD_GLOBAL | RTLD_FIRST);
+    void *handle = dlopen(file.c_str(), RTLD_LAZY | RTLD_GLOBAL);
     if (handle == NULL)
         throw OpenMMException("Error loading library "+file+": "+dlerror());
     return handle;