Fix issue #1134

Adds the necessary imports for selectors under MacOSX

lib/pure/selectors.nim

@@ -11,9 +11,12 @@
 
 import tables, os, unsigned, hashes
 
-when defined(linux): import posix, epoll
-elif defined(windows): import winlean
-else: import posix
+when defined(linux) or defined(macosx): 
+  import posix, epoll
+elif defined(windows): 
+  import winlean
+else: 
+  import posix
 
 proc hash*(x: TSocketHandle): THash {.borrow.}
 proc `$`*(x: TSocketHandle): string {.borrow.}