Optional override for RStudio dialog preference for RStudio Desktop

[paulhibbing]

In RStudio Desktop, rstudioapi dialogs are currently shown by default, with no alternative. Optionally suppressing that default would be useful in certain cases.

The get_syst function expands on the original concepts that were in the .nativeGUI methods, by allowing an override (rstudio = FALSE) that will trigger the system dialog instead of the rstudioapi dialog when RStudio Desktop is in use.

By default (rstudio = TRUE) nothing changes from the current functionality. An additional file of tests/examples has been added (manual_tests_RStudio.R) and run on Windows 10 (R 3.5.0, RStudio Desktop 1.1.447) and Ubuntu 16.04.4 (R 3.4.3, RStudio Desktop 1.1.423).

[codecov-io]

Codecov Report

Merging #2 into master will decrease coverage by 0.01%. The diff coverage is 0%.

@@           Coverage Diff            @@
##           master     #2      +/-   ##
========================================
- Coverage    1.22%   1.2%   -0.02%     
========================================
  Files           9     10       +1     
  Lines        1801   1821      +20     
========================================
  Hits           22     22              
- Misses       1779   1799      +20

Impacted Files	Coverage Δ
R/dlg_message.R	0% <0%> (ø)	:arrow_up:
R/dlg_save.R	0% <0%> (ø)	:arrow_up:
R/dlg_list.R	0% <0%> (ø)	:arrow_up:
R/dlg_dir.R	3.3% <0%> (ø)	:arrow_up:
R/dlg_open.R	0% <0%> (ø)	:arrow_up:
R/get_syst.R	0% <0%> (ø)
R/dlg_input.R	0% <0%> (ø)	:arrow_up:

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[phgrosjean]

OK for this solution, but there is one thing to correct in your PR: given the definition of the generics, which are dlg_xxx(<args>, ..., gui = .GUI), you cannot add rstudio = TRUE after gui = .GUI in the methods. You have to add it before the .... I am surprised that R CMD check does not catch it.

Could you make this correction before I incorporate your PR? Thanks.

[paulhibbing]

Done.

[phgrosjean]

Thanks, merged now.