RFR JDK-8153759: jshell tool: Smart completion detection is not reliable

[Jan Lahoda]

Hi,

When tab completion is invoked in the tool, there are two mode: "smart" 
and all/ordinary. Consecutive presses of <tab> should switch between 
these modes. But, the detection of the sequence of actions is not fully 
reliable - a tab followed by some other actions and followed by a tab 
may appear to be two consecutive tabs. This patch tries to improve the 
detection by actually watching the actions that are being performed.

Bug:
https://bugs.openjdk.java.net/browse/JDK-8153759

Webrev:
http://cr.openjdk.java.net/~jlahoda/8153759/webrev.00/

Thanks,
     Jan