cmd/oracle: usability improvements to "describe", "referrers"
cmd/oracle: usability improvements to "describe", "referrers"

Emacs integration:
- eliminate oracle minor mode
- in go-mode, bind F5, F6 to "describe", "referrers".
  This reverts a previous policy decision but convenience matters too.
- don't insist on an analysis scope for modes that don't do PTA.
- don't hide the filename as "▶"; show the last 20 chars.
  (Especially useful for "referrers" mode.)
- output postprocessing: don't get stuck in a loop if the output
  is not as expected (e.g. when it includes a panic log).

referrers:
- show the matching lines (like grep does).
  We do the I/O in parallel.

Change-Id: I86b18c1d3a4d9fa4242984cba62b314796669d8e
Reviewed-on: https://go-review.googlesource.com/8120
Reviewed-by: David Crawshaw <a2f0bf29257797dd66800b4fbb9945c3e216c004@golang.org>

emacsmirror/go-mode,dominikh/go-mode.el