Teach ddb(4) to delete to the beginning of its command line on ^U.
Teach ddb(4) to delete to the beginning of its command line on ^U.

PR:		kern/28976
Submitted by:	Nickolai Zeldovich <kolya@orbit.zepa.net>

jrobhoward/SCADAbase,jrobhoward/SCADAbase,jrobhoward/SCADAbase,jrobhoward/SCADAbase,jrobhoward/SCADAbase,jrobhoward/SCADAbase,jrobhoward/SCADAbase,jrobhoward/SCADAbase,jrobhoward/SCADAbase,jrobhoward/SCADAbase,jrobhoward/SCADAbase