make mrproper depends on a .config file?

[Jürgen Kilb]

Hi Sascha,
why does a "make mrproper" depends on a .config file?

It looks like commit 789fad984a11f63ad0728cd6eabad97b185dceea is 
responsible...

If there is a valid .config file, the problem doesn't pop up.

====
barebox-2013.01.0$ make ARCH=arm 
CROSS_COMPILE=/opt/OSELAS.Toolchain-2012.12.0/arm-cortexa9-linux-gnueabi/gcc-4.7.3-glibc-2.16.0-binutils-2.22-kernel-3.6-sanitized/bin/arm-cortexa9-linux-gnueabi- 
mrproper
make -f scripts/Makefile.clean obj=arch/arm/pbl
   HOSTCC  scripts/basic/fixdep
   HOSTCC  scripts/basic/docproc
   HOSTCC  scripts/kconfig/conf.o
   SHIPPED scripts/kconfig/zconf.tab.c
   SHIPPED scripts/kconfig/zconf.lex.c
   SHIPPED scripts/kconfig/zconf.hash.c
   HOSTCC  scripts/kconfig/zconf.tab.o
   HOSTLD  scripts/kconfig/conf
scripts/kconfig/conf --silentoldconfig Kconfig
***
*** Configuration file ".config" not found!
***
*** Please run some configurator (e.g. "make oldconfig" or
*** "make menuconfig" or "make xconfig").
***
make[3]: *** [silentoldconfig] Fehler 1
make[2]: *** [silentoldconfig] Fehler 2
   CLEAN   scripts/basic
   CLEAN   scripts/kconfig
barebox-2013.01.0$
===

greetings,
Jürgen