RFR 8180306, 8179048, 8179046, 8181950: jshell tool: /help fixes and required test fixes

[Robert Field]

Please review —

Bugs:

8180306: jshell tool: /help -- confusing identifier in feedback mode 
examples
https://bugs.openjdk.java.net/browse/JDK-8180306

8179048: jshell tool: /help -- references to "/reset or /reload" should 
add /env
https://bugs.openjdk.java.net/browse/JDK-8179048

8179046: jshell tool: /help /edit is missing -all and -start
https://bugs.openjdk.java.net/browse/JDK-8179046

8181950: jshell tests: longer help documentation breaks tests because of 
paging
https://bugs.openjdk.java.net/browse/JDK-8181950

Webrev:

http://cr.openjdk.java.net/~rfield/8180306v1.webrev/

Thanks,
Robert