Avoid using dirname; sed can do this just as well...
diff --git a/install-sh b/install-sh
index 0ff4b6a..98204c5 100755
--- a/install-sh
+++ b/install-sh
@@ -96,7 +96,8 @@
 
 # Make a temp file name in the proper directory.
 
-dstdir=`dirname $dst`
+# Avoid dirname, which doesn't exist everywhere...
+dstdir=`echo $dst | sed 's,/[^/]*$,,'`
 dsttmp=$dstdir/#inst.$$#
 
 # Move or copy the file name to the temp name