Two bugfixes regarding stale executable files, and executables changing between restarts (#689)

* service/debugger: Restore breakpoints using file:line on restart

Restoring by address can cause the breakpoint to be inserted in the
middle of an instruction if the executable file has changed.

* terminal: Warn of stale executable when printing source

service/api/types.go

@@ -313,3 +313,8 @@ func (regs Registers) String() string {
 	}
 	return buf.String()
 }
+
+type DiscardedBreakpoint struct {
+	Breakpoint *Breakpoint
+	Reason error
+}