Improve pip plugin options support

* -r, --record now looks for a local file instead of trying to cache
  the entire package index
* add --editable because it's useful
* add --single-version-externally-managed because it is too long
* add --record and --root because they're required by
  --single-version-externally-managed

plugins/pip/_pip

@@ -62,6 +62,11 @@ case "$words[1]" in
       '(--no-install)--no-install[only download packages]' \
       '(--no-download)--no-download[only install downloaded packages]' \
       '(--install-option)--install-option[extra arguments to be supplied to the setup.py]' \
+      '(--single-version-externally-managed)--single-version-externally-managed[do not download/install dependencies. requires --record or --root]'\
+      '(--root)--root[treat this path as a fake chroot, installing into it. implies --single-version-externally-managed]'\
+      '(--record)--record[file to record all installed files to.]'\
+      '(-r --requirement)'{-r,--requirement}'[requirements file]: :_files'\
+      '(-e --editable)'{-e,--editable}'[path of or url to source to link to instead of installing.]: :_files -/'\
       '1: :->packages' &&  return 0
 
       if [[ "$state" == packages ]]; then