scripts/functions: cvs retrieval first tries the mirror for tarballs

The cvs download helper looks for the local tarballs dir to see if it
can find a pre-downloaded tarball, and if it does not find it, does
the actual fetch to upstream via cvs.

In the process, it does not even try to get a tarball from the local
mirror, which can be useful if the mirror has been pre-populated
manually (or with a previously downloaded tree).

Fake a tarball get with the standard tarball-download helper, but
without specifying any upstream URL, which makes the helper directly
try the LAN mirror.

Of course, if no mirror is specified, no URL wil be available, and
the standard cvs retrieval will kick in.

Signed-off-by: "Yann E. MORIN" <yann.morin.1998@anciens.enib.fr>

 commit 608e138586993d3c59c65c2958d9a98cf0d4d1eb

 Author: Bernhard Reutner-Fischer <rep.dot.nop@gmail.com>

 Date:   Wed Jun 8 21:47:42 2011 +0200

     bump version to 0.9.32.1-git

     Signed-off-by: Bernhard Reutner-Fischer <rep.dot.nop@gmail.com>

 diff --git a/Rules.mak b/Rules.mak

 index fe06c24..a00deea 100644

 --- a/Rules.mak

 +++ b/Rules.mak

 @@ -106,7 +106,7 @@ export RUNTIME_PREFIX DEVEL_PREFIX KERNEL_HEADERS MULTILIB_DIR

  MAJOR_VERSION := 0

  MINOR_VERSION := 9

  SUBLEVEL      := 32

 -EXTRAVERSION  :=

 +EXTRAVERSION  :=.1-git

  VERSION       := $(MAJOR_VERSION).$(MINOR_VERSION).$(SUBLEVEL)

  ABI_VERSION   := $(MAJOR_VERSION)

  ifneq ($(EXTRAVERSION),)