char* -> const char* for npapis getMIMEDescription to fix build with newer mozs

extensions/source/nsplugin/source/npshell.cxx

@@ -361,7 +361,7 @@ MIMETYPE_OASIS_OPENDOCUMENT_PRESENTATION_ASCII ":odp:OpenDocument Presentation;"
 MIMETYPE_OASIS_OPENDOCUMENT_PRESENTATION_TEMPLATE_ASCII ":otp:OpenDocument Presentation Template;"
 MIMETYPE_OASIS_OPENDOCUMENT_FORMULA_ASCII ":odf:OpenDocument Formula;" );
 
-char*
+const char*
 NPP_GetMIMEDescription(void)
 {
     debug_fprintf(NSP_LOG_APPEND, "print by Netscape Plugin,  NPP_GetMIMEDescription:%s.\n", pMimeTypes);

np_sdk/inc/npapi.h

@@ -784,7 +784,7 @@ extern "C" {
 
 /* NPP_* functions are provided by the plugin and called by the navigator. */
 
-char* NPP_GetMIMEDescription(void);
+const char* NPP_GetMIMEDescription(void);
 NPError NP_LOADDS NPP_New(NPMIMEType pluginType, NPP instance,
                           uint16_t mode, int16_t argc, char* argn[],
                           char* argv[], NPSavedData* saved);