mail.c: replace deprecated g_mutex_new() with g_mutex_init() and
fix const discarded warnings.
plugins.c: gkrellm_place_plugin() change code that inserts plugins into
monitor_list to avoid compiler warnings.
Patch from Ville Skytta: fix issues flagged by cppcheck:
- netbsd.c: add some close(fd) calls before returns in gkrellm_sys_battery_init().
- winops-win32.c: add a free() in gkrellm_winop_place_gkrellm().
Bugfixes:
- chart.c: flag config modified when changing a chart's Resolution per Grid.
- fix memory leaks in multiple files: add g_thread_unref() for all GThread
pointers returned from g_thread_new() calls.