RFR: Misc fixes [v2]

[Jesper Wilhelmsson]

> - Changes casing in headers to be consistent
> - Fixed typos and minor cleanups
> - Changes all JTReg to jtreg since that's how it's written in the official documentation
> - Minor clarification in how to fix an incorrect backport

Jesper Wilhelmsson has updated the pull request incrementally with one additional commit since the last revision:

  Capitalize Mercurial

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

Changes:
  - all: https://git.openjdk.java.net/guide/pull/71/files
  - new: https://git.openjdk.java.net/guide/pull/71/files/eed2e914..46d11c21

Webrevs:
 - full: https://webrevs.openjdk.java.net/?repo=guide&pr=71&range=01
 - incr: https://webrevs.openjdk.java.net/?repo=guide&pr=71&range=00-01

  Stats: 3 lines in 1 file changed: 0 ins; 0 del; 3 mod
  Patch: https://git.openjdk.java.net/guide/pull/71.diff
  Fetch: git fetch https://git.openjdk.java.net/guide pull/71/head:pull/71

PR: https://git.openjdk.java.net/guide/pull/71