* localdir.cc: new, local package directory selection dialog; cd

* localdir.cc: new, local package directory selection dialog; cd
into selected directory
* Makefile.in (OBJS): add localdir.o
* dialog.h: add prototype for do_local_dir
* main.cc (WinMain): initialize local_dir to cwd; add call to
do_local_dir
* net.cc (dialog_cmd): make DO_LOCAL_DIR next dialog
* source.cc (dialog_cmd): ditto
* res.rc: add DO_LOCAL_DIR dialog; remove "current directory" from
presented choices in IDD_SOURCE; add IDS_ERR_CHDIR error string
* resource.h: defines for DO_LOCAL_DIR dialog; define IDS_ERR_CHDIR
* root.cc (dialog_cmd): make DO_LOCAL_DIR previous dialog
* state.h: add local_dir variable