[BRLTTY] Configure warning

[Stepan Kasal]

Hi,
  with brltty-3.10 configure says:

WARNING: package revision not known

This should be probably deactivated for a released tarball.  I'm not
suggesting a fix, perhaps you had a solution in mind...

I know that some GNU projects, e.g. Autoconf itself, use a system to
generate versions, but it is complicated and I never understood it.
(And I'm afraid that the code used inside the Autoconf project itself
depends on the fact that the VCS is git.)

One more nit; I noticed these lines:

configure.ac:
PACKAGE_REVISION="`"${srcdir}/revision" "${srcdir}"`"

revision:
revision="`svnversion -n "${sourceRoot}"`"

The outer double quotes are redundant because word splitting nor
wildcard expansion is performed on assignment, so the following would
suffice:
	variable=`"command" "prm1"`

Moreover, this form might be more portable, as there are reportedly
shells which do not correctly understand your original code.  OTOH,
the buggy shells may as well be extinct...
My source for this portability information is this:
http://www.gnu.org/software/autoconf/manual/html_node/Shell-Substitutions.html

Have a nice day,
	Stepan Kasal