Rename user_t.modem to user_t.connection

src/sbbs3/answer.cpp

src/sbbs3/chk_ar.cpp

src/sbbs3/exec.cpp

src/sbbs3/filedat.c

src/sbbs3/ftpsrvr.c

src/sbbs3/gtkuseredit/events.c

src/sbbs3/gtkuserlist/events.c

src/sbbs3/js_system.c

src/sbbs3/js_user.c

src/sbbs3/logon.cpp

src/sbbs3/newuser.cpp

src/sbbs3/sbbs.h

src/sbbs3/sbbsdefs.h

src/sbbs3/services.c

src/sbbs3/str.cpp

src/sbbs3/uedit/uedit.c

src/sbbs3/upgrade_to_v320.c

src/sbbs3/userdat.c

src/sbbs3/useredit.cpp

src/sbbs3/useredit/MainFormUnit.cpp