define safe variant of short_file_name

[kevinushey]

Pull Request Template for Rcpp

Closes #1066. This PR comes with two pieces:

1. A "safe" definition of short_file_name, defined and used explicitly in the Rcpp::debug namespace;

2. A re-worked version of the "old" (+ registered) short_file_name, which now uses a static buffer. I believe the method should be effectively un-used but I figured since it's a registered routine it's best to keep the API the same and just silence the compiler warning.

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

[eddelbuettel]

I think we once use proper deprecation.

We could "tag" the older unsafer variant and say it'll go in, say, 12 month. Thoughts? (That is somewhat orthogonal to the PR though of course not fully...)

[kevinushey]

I don't have any strong feelings re: deprecation -- I'll let you make the call. I expect removing it would go smoothly, but experience has taught me to always expect surprises.

[codecov-io]

Codecov Report

Merging #1067 into master will not change coverage by %.
The diff coverage is n/a.

@@           Coverage Diff           @@
##           master    #1067   +/-   ##
=======================================
  Coverage   95.61%   95.61%           
=======================================
  Files          64       64           
  Lines        2782     2782           
=======================================
  Hits         2660     2660           
  Misses        122      122           

Impacted Files	Coverage Δ
src/api.cpp	100.00% <ø> (ø)