limit tests to 4GB of memory.
3G works on thresher, 2G does not

R=r
OCL=14956
CL=14958
diff --git a/test/run b/test/run
index dd24312..8013efe 100755
--- a/test/run
+++ b/test/run
@@ -23,6 +23,10 @@
 TMP1FILE=/tmp/gotest1-$USER
 TMP2FILE=/tmp/gotest2-$USER
 
+# don't run the machine out of memory: limit individual processes to 4GB.
+# on thresher, 3GB suffices to run the tests; with 2GB, peano fails.
+ulimit -v 4000000
+
 for dir in . ken chan bugs fixedbugs
 do
 	for i in $dir/*.go