RFR: 8153761: JShell: Completion -- Show parameter names if possible

[Jan Lahoda]

Hi,

JBS: https://bugs.openjdk.java.net/browse/JDK-8153761

Webrev:
http://cr.openjdk.java.net/~jlahoda/8153761/webrev.00/index.html

Currently, when showing the synopsis of methods (Shift-<tab>), 
synthesised, not real, parameter names are shown. This patches improves 
that by:
-reading the parameter names from the classfiles if they are available 
(by using "-XDsave-parameter-names=true")
-storing parameter names when compiling user's snippets (by using 
"-parameters")
-looking for src.zip in the JDK installation if the parameter names are 
not available in the classfiles, and reading the parameter names from 
the sources.

Comments are welcome!

Jan