gistfile1.txt

df2 %>% rename_(.dots=setNames(names(.), (gsub("X", "", names(.)))))

## Source: local data frame [7 x 4]
## 
##          GDP.per.capita        1800        1801        1802
##                   (chr)       (chr)       (chr)       (chr)
## 1              Abkhazia          NA          NA          NA
## 2           Afghanistan 634.4000136 634.4000136 634.4000136
## 3 Akrotiri and Dhekelia          NA          NA          NA
## 4               Albania 860.5879664 861.4817538 862.3764694
## 5               Algeria        1360 1361.635788 1363.271576
## 6        American Samoa          NA          NA          NA
## 7               Andorra        1260     1262.15      1264.3