build: unify mesa version by using a VERSION file

Rather than having to keep track of all the build systems and their respecitve
definition of the mesa version, use a single top file VERSION. Every build
system is responsible for reading/parsing the file and using it

v2:
* remove useless bulletpoint from the documentation, suggested by Matt
* "Androing is Linux. Use '/' in stead of '\'", spotted by Chad V
* use cleaner code to get the version in scons, suggested by Chad V

v3:
* ensure leading and trailing whitespace characters are stripped while parsing
* android: handle GNU shell commands approapriately

Reviewed-by: Matt Turner <mattst88@gmail.com>
Reviewed-by: Chad Versace <chad.versace@linux.intel.com>
Reviewed-by: Kenneth Graunke <kenneth@whitecape.org>
Signed-off-by: Emil Velikov <emil.l.velikov@gmail.com>
diff --git a/configure.ac b/configure.ac
index 425b6ee..62d06e0 100644
--- a/configure.ac
+++ b/configure.ac
@@ -6,7 +6,8 @@
 m4_divert_once([HELP_END], [
 See docs/autoconf.html for more details on the options for Mesa.])
 
-AC_INIT([Mesa], [9.3.0-devel],
+m4_define(MESA_VERSION, m4_normalize(m4_include(VERSION)))
+AC_INIT([Mesa], [MESA_VERSION],
     [https://bugs.freedesktop.org/enter_bug.cgi?product=Mesa])
 AC_CONFIG_AUX_DIR([bin])
 AC_CONFIG_MACRO_DIR([m4])