Fix some sed bugs and improve error reporting.

Fix some sed bugs and improve error reporting.

A newline after 'b' commands in -e command line patterns was being discarded
as whitespace, a single element regex match on a {} was leaving stale state
for the next line, and giant -e blobs of instructions were saying things
like problem at character 432 (note: nulls inserted for regex processing
aren't always cleaned up, screws up error reporting).