fix for potential read builtin crash if bash gets a signal before read reads any input; make wait -f work if there are no pid or job arguments and update documentation; save and restore variable reflected in $BASH_COMMAND around shell function calls

doc/bash.1

@@ -13038,6 +13038,8 @@ This is useful only when used with the \fB\-n\fP option.
 Supplying the \fB\-f\fP option, when job control is enabled,
 forces \fBwait\fP to wait for each \fIid\fP to terminate before
 returning its status, instead of returning when it changes status.
+If there are no \fIid\fP arguments,
+\fBwait\fP waits until all background processes have terminated.
 .IP
 If none of the \fIid\fPs specify one of the shell's active child
 processes, the return status is 127.