Functions/Zle/copy-earlier-word: Enhance insert-last-word to
pick different lines from the history (including the current
line) and different words from that line. Add copy-earlier-word
as suggested by Dominik Vogt to copy words from either the
current line, or (following an insert-last-word) a previous
history line.
Also changed it to not accept the line if the infer fails. Ignore
transient edits in the history when searching for an inference and
grabbing the next line (affecting acceptandinfernexthistory(),
infernexthistory(), and acceptlineanddownhistory()).
