tagQuery(): Speed enhancements and consistent tag name order

[schloerke]

(Similar to) before:

Now:

• mget() is MUCH faster than as.list.environment() and shuffling the elements.
• Also removed usage of setdiff() if favor of wrapper to x[match(x, y, 0L) == 0L] to avoid a call to unique()
• Adjusted some lapply calls to for-loops to avoid lapply overhead
• Adjusted some walk calls to for-loops to avoid usage of <<-

[wch]

I don't know if performance is an issue in this code, but if it is, have you considered using mget()?

e <- new.env()
e$a <- 1
e$b <- 2
e$c <- 3

mget(c("c", "a"), e)
#> $c
#> [1] 3
#> 
#> $a
#> [1] 1

(I don't know if mget() is actually faster though -- it's worth testing)