update to use collectSeq

Author: dsyme

src/FSharp.Control.AsyncSeq/AsyncSeq.fs

@@ -579,7 +579,7 @@ module AsyncSeq =
         if box resource <> null then dispose resource)
 
     member x.For (seq:seq<'T>, action:'T -> AsyncSeq<'TResult>) = 
-      collect action (ofSeq seq) 
+      collectSeq action seq
 
     member x.For (seq:AsyncSeq<'T>, action:'T -> AsyncSeq<'TResult>) = 
       collect action seq

tests/FSharp.Control.AsyncSeq.Tests/AsyncSeqTests.fs

@@ -742,6 +742,9 @@ let perfTest2 n =
 //perfTest2 1000000         0.663
 
 
+// This was the original ofSeq implementation.  It is now faster than before this perf testing
+// took place, but is still slower than the bespoke ofSeq implementation (which effectively "knows"
+// that a single yield happens for each iteration of the loop).
 let ofSeq2 (source : seq<'T>) = asyncSeq {  
     for el in source do   
       yield el }  
@@ -760,4 +763,4 @@ let perfTest3 n =
 //perfTest3 5000           0.009
 //perfTest3 10000           0.015
 //perfTest3 100000          0.155
-//perfTest3 1000000         1.645
+//perfTest3 1000000         1.500