R ancient job fails

[jangorecki]

https://rdatatable.gitlab.io/data.table/web/checks/data.table/test-lin-ancient-cran/00check.log

* checking R code for possible problems ... NOTE
frollapply : <anonymous>: no visible global function definition for
  ‘suspendInterrupts’
Undefined global functions or variables:
  suspendInterrupts

Test 2336.3 produced 1 warnings but expected 0
  Expected: 
  Observed: Incompatible methods ("-.Date", "-.IDate") for "-"
  Test 2336.4 produced 1 warnings but expected 0
  Expected: 
  Observed: Incompatible methods ("-.Date", "-.IDate") for "-"
  Test 2336.5 produced 1 warnings but expected 0
  Expected: 
  Observed: Incompatible methods ("-.IDate", "-.Date") for "-"
  Test 2336.6 produced 1 warnings but expected 0
  Expected: 
  Observed: Incompatible methods ("-.IDate", "-.Date") for "-"
  V1
  1
  V1
  0,1
  0,2
  a,b
  a

I will take care of the first one.

[MichaelChirico]

the latter should just be skipped, the warning is expected & unavoidable on old R as I understand it.