basic thread support; still broken on Windows; untested on Mac OS X

tests/gc/tthreads.nim

@@ -0,0 +1,21 @@
+
+import threads
+
+var
+  thr: array [0..4, TThread]
+  L: TLock
+  
+proc threadFunc(c: pointer) {.procvar.} = 
+  for i in 0..9: 
+    Aquire(L)
+    echo i
+    Release(L)
+
+InitLock(L)
+
+for i in 0..high(thr):
+  createThread(thr[i], threadFunc)
+for i in 0..high(thr):
+  joinThread(thr[i])
+
+