tools: fix libtool version check for Debian

On Debian, the libtool version is prefixed by "Debian-":

    $ libtool --version | head -1
    libtool (GNU libtool) 2.5.4 Debian-2.5.4-4

As a consequence, the extracted version is incorrect:

    $ libtool --version | head -1 | sed s/'.* '//
    Debian-2.5.4-4

causing the bootstrap script to fail:

    ./bootstrap: 31: [: Illegal number: Debian-2
    ./bootstrap: 32: [: Illegal number: Debian-2
    ./bootstrap: 33: [: Illegal number: Debian-2

Extract the first pattern matching NUM.NUM or NUM.NUM.NUM.

extras/tools/bootstrap

@@ -128,7 +128,7 @@ else
     if [ -z "$2" ];then
         FOUND="$FOUND $1"
     else
-        gotver=`$1 --version | head -1 | sed s/'.* '//`
+        gotver=`$1 --version | head -1 | grep -o '[0-9]\+\.[0-9]\+\(\.[0-9]\+\)\?' | head -1`
         check_version $1 $gotver $2
     fi
 fi