Implemented .WAITHEADmaster

Based on this patch:
http://lists.gnu.org/archive/html/help-make/2005-04/msg00091.html

Test file (wait.mk):
simple: 1 .WAIT 2
    @echo $@
1:
    @sleep 2; echo $@
2:
    @echo $@

run:
./make --sun -f wait.mk -j50 simple
Output:
1
2
simple

1 files changed, 1 insertions, 0 deletions

diff --git a/dep.h b/dep.h
index b8c0d29..7551e63 100644
--- a/dep.h
+++ b/dep.h
@@ -42,6 +42,7 @@ struct dep
     unsigned int staticpattern : 1;
     unsigned int need_2nd_expansion : 1;
     unsigned int dontcare : 1;
+    unsigned int wait : 1;
   };