Please issue a warning in FromDataFrameNetwork() when it deletes duplicates

[telenskyt]

The function FromDataFrameNetwork() deletes duplicated nodes silently without issuing a warning, even when check = "check", which, according to the documentation:

"check": if the name conformance should be checked and warnings should be printed in case of non-conformance (the default)

But currently it doesn't print any warnings, see:

library(data.tree)

d <- data.frame(node = c("a", "b", "c", "a"), parent = c("/", "a", "a", "/"))
d

  node parent
1    a      /
2    b      a
3    c      a
4    a      /

x <- FromDataFrameNetwork(d, check = "check") # no warnings printed
print(x)

     levelName
1              
2  ¦--a        
3  ¦   ¦--b    
4  ¦   ¦   °--c
5  ¦   °--d    
6  °--b 

The duplicated node "a" was silently removed without warnings. I believe this warning should be printed out, because now I missed this problem in my data and then my other workaround didn't work (#179).

Tested on data.tree package version 1.2.0.