Add echo parameter to sourcecpp

[eddelbuettel]

This is a twoofer which cleans up the earlier #1126 with a new parameter echo that defaults to TRUE (old behaviour) and is passed on to source() to make any optional R code submitted to sourceCpp() or cppFunction() silent. It also cleans up the simple DataFrame warning in #1137.

Checklist

• Code compiles correctly
• R CMD check still passes all tests
• Prefereably, new tests were added which fail without the change
• Document the changes by file in ChangeLog

[kevinushey]

LGTM!

[eddelbuettel]

Yes, it's slowly churning through yet another rev.dep run and of course no issues there either. May wait, or may merge sooner. Thanks for the thumbs-up.

[eddelbuettel]

Uneventfule rev.dep run, as expected: RcppCore/rcpp-logs@223d559 so merging now.