RFR: Improve "git pr help" [v3]

[Magnus Ihse Bursie]

> The help texts were never shown for the "git pr" sub-commands.

Magnus Ihse Bursie has updated the pull request incrementally with one additional commit since the last revision:

  Fix merge error

-------------

Changes:
  - all: https://git.openjdk.java.net/skara/pull/778/files
  - new: https://git.openjdk.java.net/skara/pull/778/files/2da6890f..c0787c92

Webrevs:
 - full: https://webrevs.openjdk.java.net/?repo=skara&pr=778&range=02
 - incr: https://webrevs.openjdk.java.net/?repo=skara&pr=778&range=01-02

  Stats: 1 line in 1 file changed: 0 ins; 0 del; 1 mod
  Patch: https://git.openjdk.java.net/skara/pull/778.diff
  Fetch: git fetch https://git.openjdk.java.net/skara pull/778/head:pull/778

PR: https://git.openjdk.java.net/skara/pull/778