It is a burden to create /*/bin/disk or /*/bin/dir_for_your_new_tool,
and it is easier if mk install creates the BIN directory.
A minor problem is that if you make a mistake you are going to create
a directory that should not be there; but in that case you can remove it.

Reference: /n/sources/patch/maybe/mkinstall-mkdir
Date: Thu Mar 14 19:38:24 CET 2013
Signed-off-by: nemo@lsub.org

--- /sys/src/cmd/mkone	Thu Mar 14 19:37:07 2013
+++ /sys/src/cmd/mkone	Thu Mar 14 19:37:03 2013
@@ -26,6 +26,7 @@
 install:V:	$BIN/$TARG
 
 $BIN/$TARG:	$O.out
+	test -d $BIN || mkdir -p $BIN
 	cp $prereq $BIN/$TARG
 
 installall:V:
--- /sys/src/cmd/mkmany	Thu Mar 14 19:37:15 2013
+++ /sys/src/cmd/mkmany	Thu Mar 14 19:37:10 2013
@@ -28,6 +28,7 @@
 %.install:V:	$BIN/%
 
 $BIN/%:	$O.%
+	test -d $BIN || mkdir -p $BIN
 	cp $O.$stem $BIN/$stem
 
 %.installall:V: