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In particular, it should no longer be necessary to patch the makefile
for hassle-free compilation.

The targets are:
make export
make tarball
Both preserve svn revisions and the exported tree does not depend on
subversion in any way or shape.

Documentation for this feature has been added to README.

We need this for five reasons:
1. Packagers currently have to patch flashrom source to compile it on
systems without subversion. We should make it easier for them.
2. Snapshot tarballs currently have a .svn 1.5 directory included but
this will cause errors for users with older svn 1.4. Not requiring
subversion for snapshot compilation is best.
3. Since packagers seldom the svn revision in their fixup patches, some
packages out there have incorrect or no revision, only major version
numbers.
4. Releasing a new version of flashrom needs too many changes to the
makefile which have to be reverted instantly after the release. That is
unnecessary churn.
5. Making a release is easy with the change. Update the major version,
then run "make tarball".

Corresponding to flashrom svn r587.

Signed-off-by: Carl-Daniel Hailfinger <c-d.hailfinger.devel.2006@gmx.net>  
Acked-by: Uwe Hermann <uwe@hermann-uwe.de>