core: add priority in plugins to initialize them in order

Current order is: charset, logger, exec, trigger, aspell, alias, fifo, xfer,
irc, relay, guile/lua/perl/python/ruby/tcl, script.

src/plugins/exec/exec.c

@@ -37,6 +37,7 @@ WEECHAT_PLUGIN_DESCRIPTION(N_("Execution of external commands in WeeChat"));
 WEECHAT_PLUGIN_AUTHOR("Sébastien Helleu <flashcode@flashtux.org>");
 WEECHAT_PLUGIN_VERSION(WEECHAT_VERSION);
 WEECHAT_PLUGIN_LICENSE(WEECHAT_LICENSE);
+WEECHAT_PLUGIN_PRIORITY(11000);
 
 struct t_weechat_plugin *weechat_exec_plugin = NULL;