Require Alure 1.2 and use the new ALURE_VERSION_STRING for version detection

This version comes with a few very important fixes. Just let me mention some of
them:
* Fixed potential lockup when the library is shutdown with streams open.
* Added ALURE_VERSION* macros to detect the version being compiled with. -> This
way, we can properly detect the ALURE versions and provide a more safer error
message than previously
* Introduced alureGetStreamLength to get the approximate number of
samples in a stream, if known. -> We could properly eliminate the sndfile direct
dependency
* The vorbisfile codec now works with libvorbisidec, for
Tremor support. -> We can get proper support for that format in case of
Harmattan/Maemo6 and probably other targets as well
* Compilation now uses a version script on
non-Windows, non-Apple systems to better control the
exported functions.
* Improved detection for OpenAL and some support libs during compilation. -> It
now works properly on Windows because of this change I proposed against alure.

Here you can find the announcement email for further details:
http://opensource.creative.com/pipermail/openal/2011-July/012433.html

I have just updated the installation page on our website as well.
There has been an available binary package in Archlinux, Harmattan/Maemo6,
Fedora right away, but the other packagers were also notified. It depends only
on them. At any rate, it is really simple to get it built locally as well since
it is a very small code base. Follow the instructions on the following link:
http://kcat.strangesoft.net/alure.html#download

Summary: Couple of cross-platform fixes for Windows, Harmattan and so forth
along with other fixes as well. Also, the FindAlure.cmake module is smarter this
time.