Data.table: dec ='，'时，fread可能无法解析有效文件

很棒的包装！ 谢谢你。
巧合的是，昨天我经历了一种与恐惧有关的奇怪行为。
这是一个简单的示例（来自对一堆文件使用lapply fread的实际案例）。

library(data.table)

DT = data.table(A = rep("20,1", 1e4))
fwrite(DT, "DT.csv", quote = FALSE)

classA = character(1e3)

for (i in seq_along(classA)) {

  DT = fread("DT.csv", sep = ";", dec = ",", colClasses = "numeric")
  classA[i] = DT[, class(A)]
}

table(classA)

这给了我：

Warning message:
In fread("DT.csv", sep = ";", dec = ",", colClasses = "numeric",  :
  Bumped column 1 to type character on data row 387, field contains '20,1'. Coercing previously read values in this column from logical, integer or numeric back to character which may not be lossless; e.g., if '00' and '000' occurred before they will now be just '0', and there may be inconsistencies with treatment of ',,' and ',NA,' too (if they occurred in this column before the bump). If this matters please rerun and set 'colClasses' to 'character' for this column. Please note that column type detection uses a sample of 1,000 rows (100 rows at 10 points) so hopefully this message should be very rare. If reporting to datatable-help, please rerun and include the output from verbose=TRUE.

table(classA)
# classA
# character   numeric 
#        1       999 
which(classA == "character")
# [1] 9
`````

So, sometimes, the column is read as character with the spotted row index being different for different runs. And the ```which``` indicates it is more likely to happen in the first iterations. I don't get the randomness and the fact that colClasses is ignored (I set colClasses after reading fread doc...).
And... I did not manage to reproduce the error when setting verbose = TRUE... Also, the bug was observed using RStudio, not reproduced in the R console...
Sorry if I missed or misunderstood something...

```r
sessionInfo()
R version 3.3.2 (2016-10-31)
Platform: x86_64-w64-mingw32/x64 (64-bit)
Running under: Windows 7 x64 (build 7601) Service Pack 1

locale:
[1] LC_COLLATE=English_United States.1252  LC_CTYPE=English_United States.1252   
[3] LC_MONETARY=English_United States.1252 LC_NUMERIC=C                          
[5] LC_TIME=English_United States.1252    

attached base packages:
[1] stats     graphics  grDevices utils     datasets  methods   base     

other attached packages:
[1] data.table_1.10.4-3

loaded via a namespace (and not attached):
[1] tools_3.3.2 yaml_2.1.18

请确保更新到data.table的开发版本，然后再次进行测试。 自上次发布以来，对fread进行了很多改进

确实...用1.10.5多次运行相同的示例，效果很好。
谢谢你。