gitk: Fix bug in parsing multiple revision arguments

If the user specified multiple revisions arguments on the command
line or for a view, we were passing the whole list of arguments to
git rev-parse as a single argument, and thus git rev-parse didn't
interpret it as revisions.  This fixes it by adding an eval so the
arguments get passed to git rev-parse as separate arguments.

Signed-off-by: Paul Mackerras <paulus@samba.org>
diff --git a/gitk b/gitk
index e0eb3d0..46f9a35 100755
--- a/gitk
+++ b/gitk
@@ -106,7 +106,7 @@
     set vnextroot($view) 0
     varcinit $view
 
-    set commits [exec git rev-parse --default HEAD --revs-only \
+    set commits [eval exec git rev-parse --default HEAD --revs-only \
 		     $viewargs($view)]
     set viewincl($view) {}
     foreach c $commits {